Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Active materials are a subset of soft matter that is constantly being driven out of an equilibrium state due to the energy input from internal processes such as the hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP), as found in biological systems. Firstly, we construct and study a simple model of a flexible filament with an active crosslinker/molecular motor. We treat the system on a mesoscopic scale using a Langevin equation approach, which we analyse via a functional integral approach using the Martin-Siggia-Rose formalism. We characterise the steady state behaviour of the system up to first order in the motor force and also the autocorrelation of fluctuations of the position of the active crosslink on the filament. We find that this autocorrelation function does not depend on the motor force up to first order for the case where the crosslinker is located in the middle of the contour length of the filament. Properties that characterise the elastic response of the system are studied and found to scale with the autocorrelation of fluctuations of the active crosslink position. Secondly, we give a brief overview of the current state of dynamical polymer network theory and then propose two dynamical network models based on a Cayley-tree topology. Our first model takes a renormalisation approach and derive recurrence relations for the coupling constants of the system. The second model builds on the ideas of an Edwards type network theory where Wick’s theorem is employed to enforce the constraint conditions. Both models are examined using a functional integral approach. / AFRIKAANSE OPSOMMING: Aktiewe stelsels is ’n subveld van sagte materie fisika wat handel oor sisteme wat uit ekwilibruim gedryf word deur middel van interne prossesse, soos wat gevind word in biologiese stelsels. Eerstens konstruëer en bestudeer ons ’n model vir ’n buigbare filament met ’n aktiewe kruisskakelaar of molekulêre motor. Ons formuleer die stelsel op ’n mesoskopiese skaal deur gebruik te maak van ’n Langevin vergelyking formalisme en bestudeer die stelsel deur gebruik te maak van funksionaal integraal metodes deur middel van die Martin-Siggia-Rose formalisme. Dit laat ons in staat om die tydonafhankle gedrag van die stelsel te bestudeer tot op eerste orde in die motorkrag. Ons is ook in staat om die outokorrelasie fluktuasies van die posisie van die aktiewe kruisskakelaar te karakteriseer. Ons vind dat die outokorrelasie onafhanklink is van die motorkrag tot eerste orde in die geval waar die kruisskakelaar in die middel van die filament geleë is. Die elastiese eienksappe van die sisteem word ook ondersoek en gevind dat die skaleer soos die outokorrelasie van die fluktuasies van die aktiewe kruisskakelaar posisie. Tweedens gee ons ’n vlugtige oorsig van die huidige toestand van dinamiese polimeer netwerk teorie en stel dan ons eie twee modelle voor wat gebasseer is op ’n Caylee-boom topologie. Ons eerste model maak gebruik van ’n hernormering beginsel en dit laat ons toe om rekurrensierelasies vir die koppelingskonstates te verkry. Die tweede model bou op idees van ’n Edwards tipe netwerk teorie waar Wick se teorema ingespan word om die beperkingskondisies af te dwing. Beide modelle word met funksionaal integraal metodes bestudeer.

Thesis (MSc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: We construct and study a simple model for an active gel of exible polymer filaments crosslinked by a molecular motor cluster that perform reversible work while translating along the filaments. The filament end points are crosslinked to an elastic background. In this sense we employ a simplified model for motor clusters that act as slipping links that exert force while moving along the strands. Using the framework of replica theory, quenched averages are taken over the disorder which originates from permanent random crosslinking of network end points to the background. We investigate how a small motor force contributes to the elastic properties of the network. We learn that in addition to the normal elastic response for the network there is an extra contribution to the network elasticity from the motor activity. This depends on the ratio of the entropic spring constant for the linked bio-polymerchain to the spring constant of the tether of the motor. / AFRIKAANSE OPSOMMING: Ons konstrueer en bestudeer 'n eenvoudige model vir 'n aktiewe netwerk van eksieble polimeerfilamente wat deur grosse van molekulere motors aan mekaar verbind word wat omkeerbare werk doen terwyl dit langs die filamente transleer. Die eindpunte van die filamente is aan 'n elastiese agtergrond verbind. In hierdie sin benut ons 'n eenvoudige model vir motorclusters wat as verskuifbare verbindings krag op die filamente tydens beweging kan uitoefen. Nie-termiese wanorde gemiddeldes word geneem oor die wanorde wat deur die lukrake permanente verbindings van netwerk eindpunte aan die agtergrond veroorsaak word. Ons ondersoek hoe 'n klein motorkrag tot die elastiese eienskappe van die netwerk bydra. Ons leer dat daar bo en behalwe die gewone elastiese respons vir die netwerk 'n elastiese bydrae as gevolg van die motors se aktiwiteit voorkom. Dit hang af van die verhouding van die entropiese veerkonstante van die biopolimerketting tot die veerkonstante van die anker van die motor.

<p>E-business provides important opportunities of trade for businesses, and the supporting business system must handle this environment efficiently. One current trend in business systems is to move business logic, such as business processes and business rules, out from the application logic and into separate support systems. The reason to make this separation is to increase the agility of the business, to make the system able to change more rapidly when the business situation changes.</p><p>This report focus on business rules enforced in business rule engines. Specific interest is on how such rule engines meet the requirements of the e-business domain. The report presents an overview of business rule engines. Five general categories of characteristics are proposed. The proposed characteristics are then used in a comparison of three business rule engines.</p>

E-business provides important opportunities of trade for businesses, and the supporting business system must handle this environment efficiently. One current trend in business systems is to move business logic, such as business processes and business rules, out from the application logic and into separate support systems. The reason to make this separation is to increase the agility of the business, to make the system able to change more rapidly when the business situation changes. This report focus on business rules enforced in business rule engines. Specific interest is on how such rule engines meet the requirements of the e-business domain. The report presents an overview of business rule engines. Five general categories of characteristics are proposed. The proposed characteristics are then used in a comparison of three business rule engines.

The goal of this thesis work is to evaluate and quantify the advantages and disadvantages of Active Rear Steering (ARS). The evaluation is carried out through Multi-Body System (MBS) simulations. An analytical model has been developed to better understand the basic dynamics of vehicles equipped with rear steering. In parallel, a high fidelity MBS model is developed in Simpack. This model includes suspension kinematics and compliance, allowing for detailed analyses of steering hardware performance. Next, different control strategies aiming at improving manoeuvrability, stability and agility are implemented in Simulink. In order to assess their effectiveness, the high fidelity model is utilised by running co-simulation with Simulink. Manoeuvrability is assessed through constant steer, constant radius and ramp steer manoeuvres. Stability is assessed through transient manoeuvres such as step steer and sine with dwell. Agility is assessed through step steer and frequency response. Ultimately, also a subjective assessment is carried out by means of Volvo Cars' dynamic driving simulator. The conclusion from the assessment is that the drivers feel the all wheel steered vehicle more stable during evasive manoeuvres. It is concluded that for manoeuvrability the minimum turning radius is reduced by 19 % at low velocity; this implies that the steering angle request is reduced at low velocity, while it is increased at high velocity. A slightly higher steering angle request at high velocity might be beneficial since the driver would be able to control the vehicle in a wider range of steering wheel angles. For agility the results are contradicting: on the one hand, according to the step steer rise time difference between lateral acceleration and yaw rate, the controlled vehicles are performing worse than the passive vehicle; on the other hand, according to the frequency response analysis, both the delays between steering input and yaw rate and between lateral acceleration and yaw rate are reduced up to respectively 75 % and 46 % for the considered frequency range. Finally, for stability, the yaw rate overshoot from a step steer can be reduced up to 65 % at high velocity and the sideslip angle can always be reduced. The vehicle equipped with ARS outperforms the passive vehicle in the sine with dwell manoeuvre. / Målet med detta examensarbete är att utvärdera och kvantifiera fördelarna och nackdelarna med Active Rear Steer (ARS) för Volvo Cars. Utvärderingen utförs genom Multi-Body System (MBS) simuleringar. En analytisk modell har utvecklats för att bättre förstå den grundläggande dynamiken i fordon utrustade med bakhjulsstyrning. Parallelt utvecklades en MBS-modell med hög precision i Simpack. Denna modell inkluderar hjulupphängningens kinematik och eftergivlighet, vilket möjliggör detaljerade analyser av styrhårdvarans prestanda. Därefter implementeras olika kontrollstrategier som syftar till att förbättra manövrerbarhet, stabilitet och agilitet i Simulink. För att bedöma deras effektivitet används MBS-modellen för att köra co-simulering med Simulink.Manövrerbarhet bedöms genom konstant styrning, konstant radie och rampstyrning. Stabilitet bedöms genom transienta manövrar som stegstyrning och sinus med fördröjning. Agilitet bedöms genom stegstyrning och frekvensrespons. Slutligen görs också en subjektiv bedömning med hjälp av Volvo Cars dynamiska körsimulator. Slutsatsen från bedömningen är att förarna anser att fordonet upplevs vara mycket stabilare vid undanmanövrar. Vidare är slutsatsen att för manövrerbarhet minskar den minsta svängradien med 19 % vid mycket låg hastighet; detta innebär att styrvinkel reduceras vid låg hastighet, medan den ökar vid hög hastighet. En något högre styrvinkeln kan vara fördelaktig eftersom föraren skulle kunna styra fordonet i ett större rattvinkelområde. För agilitet är resultaten motsägelsefulla: å ena sidan, enligt stegstyrningstidsskillnaden mellan lateral acceleration och girhastighet, fungerar de aktiva fordonen sämre än det passiva fordonet; å andra sidan, enligt frekvensresponsanalysen, reduceras både fördröjningarna mellan girhastighet och styrvinkel och mellan lateral acceleration och girhastighet upp till ungefär 30 %. Slutligen, för stabilitet, kan girhastighetens översläng från en stegstyrning minskas upp till 65 % vid hög hastighet och avdriftsvinkeln kan alltid minskas. Fordonet som är utrustat med ARS överträffar det passiva fordonet i manövern sinus med fördröjning.