Thesis (MSc)--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

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.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis I study compact objects described by the Manko-Novikov spacetime. The Manko- Novikov spacetime is an exact solution to the Einstein Field Equations that allows objects to be black hole-like, but with a multipole structure di erent from Kerr black holes. The aim of the research is to investigate whether we will observationally be able to tell these bumpy black holes, if they exist, apart from traditional Kerr black holes. I explore the geodesic motion of a test probe in the Manko-Novikov spacetime. I quantify the motion using Poincar e maps and rotation curves. The Manko-Novikov spacetime admits regions with regular motion as well as regions with chaotic motion. The occurrence of chaos is correlated with orbits for which the characteristic frequencies are resonant. The new result presented in this thesis is a global characterisation of where resonances and thus chaos are likely to occur for all orbits. These calculations are performed in the Kerr spacetime, from which I obtain that low order resonances occur within 20 Schwarzschild radii (or 40M) of the compact object with mass M. By the KAM theorem, the occurrence of chaos is therefore limited to this region for all small perturbations from Kerr. These resonant events will be measurable in the Galactic Centre using eLISA. This con nement of low order resonances indicates that the frequency values of orbits of radii well outside of 20 Schwarzschild radii can be approximated using canonical perturbation theory. / AFRIKAANSE OPSOMMING: In hierdie tesis word kompakte voorwerpe bestudeer soos omskryf deur die Manko-Novikov ruimtetyd. Die Manko-Novikov ruimtetyd is 'n eksakte oplossing van die Einstein Veldvergelykings. Die Manko-Novikov ruimtetyd formuleer gravitasiekolk-tipe voorwerpe waarvan die veelpool-struktuur afwyk van die tradisionele Kerr gravitasiekolk-struktuur. Die oogmerk van die navorsing is om vas te stel of ons met behulp van waarnemings hierdie bonkige gravitasiekolke van die tradisionele Kerr gravitasiekolke kan onderskei. Ek ondersoek die geodetiese beweging van 'n toetsmassa in die Manko-Novikov ruimtetyd. Die beweging word gekwanti seer met behulp van Poincar e afbeeldings en rotasiekrommes. In die Manko-Novikov ruimtetyd identi seer ek gebiede waarbinne re elmatige beweging voorkom asook gebiede waarbinne chaotiese bane voorkom. Die ontstaan van chaos word geassosieer met bane waarvan die fundamentele frekwensies resonant is. 'n Nuwe resultaat wat in hierdie tesis voorgehou word behels 'n globale karakterisering wat aandui waar resonansies en dus chaos na alle waarskynlikheid voorkom. Laasgenoemde berekeninge word vir die Kerr ruimtetyd uitgevoer. Hierdeur toon ek alle lae orde resonansies kom voor binne 20 Schwarzschild radii (of 40M) vanaf die kompakte voorwerp met mass M. Die KAM Stelling bepaal dan dat vir alle klein steurings toegepas op die Kerr ruimtetyd die voorkoms van chaos beperk sal wees tot bogenoemde gebied. Die resonansies binne hierdie gebied sal deur eLISA in die sentrum van die melkwegstelsel gemeet kan word. Hierdie beperking van lae orde resonansies tot 'n sekere afstand vanaf die kompakte voorwerp verseker dat die frekwensies van bane wat buite hierdie gebied val, akkuraat deur kanoniese steuringsteorie bepaal kan word.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The demand for renewable energy sources has grown out of the humanity’s increasing need for electricity as well as depleting fossil fuel reserves. Organic-dye sensitised solar cells were developed as a green, cost-effective alternative to the market-dominating silicon solar cell technology. The field of photovoltaic devices and organic-DSSCs is interesting because we want to develop better, more efficient cells at lower costs using environmentally friendly materials. By studying the fundamental physics and chemistry processes occurring during and after the interaction of light with these devices, we create a window into the mechanism of photosynthesis. Our DSSCs were prepared by sensitisation of highly porous ZnO with different indoline dyes containing the same chromophore, but different alkyl chain lengths bonded to one of two carboxyl anchors as: DN91 (1 C) < DN216 (5 C) < DN285 (10 C). The role of the dye molecules is to absorb photons and donate electrons to the ZnO which acts as the charge acceptor, at the dye|ZnO interface. Through photoelectrochemical characterisation it was found that the structure of the dyes has an effect on the maximum current (JSC) produced by the cells: the shorter the alkyl chain, the higher the JSC. This macroscopic investigation was complimented by microscopic measurements in the form of transient absorption spectroscopy. This allows us to follow, in real time, the photoinduced oxidation of the dye and its regeneration occurring through desired and undesired pathways. It was found that the injection efficiencies of the dye molecules were directly responsible for the trend in the short circuit currents. / AFRIKAANSE OPSOMMING: Die aanvraag na die ontwikkeling van herwinbare energie bronne spruit voort uit die voorsienbare uitputting van fossiel brandstof bronne sowel as die groeiende behoefte om aan die mensdom se elektrisiteit behoeftes te voldoen. Kleurstof gesensitiseerde sonselle is ontwikkel as ’n groen, koste-effektiewe alternatief tot die silikon sonsel tegnologie wat die mark domineer. Die fotovoltaïse toestel veld, spesifiek organiese kleurstof gesensitiseerde sonselle is interessant omdat daar ruimte bestaan vir die ontwikkeling van beter meer effektiewe selle in terme van vervaardigings koste en prosesse wat omgewingsvriendelik is. Deur die fundamentele fisika en chemiese prosesse wat plaas vind tydens en na lig interaksie met hierdie selle te bestudeer gee dit insig oor die werkingsmeganisme van fotosintese. Ons kleurstof gesensitiseerde sonselle is voorberei deur sensitasie van hoogs poreuse ZnO met verskillende indolien kleurstowwe wat dieselfde kromofoor bevat wat met verskillende alkiel ketting lengtes verbind is aan een van twee karboksiel ankers as: DN91 (1 C) < DN216 (5 C) < DN285 (10 C). Die rol van die kleurstof molekules is om fotone te absorbeer en elektrone te doneer aan die ZnO wat as die lading akseptor dien by die kleurstof|ZnO intervlak. Deur fotoelektrochemiese karakterisasie is bevind dat die struktuur van die kleurstof ’n effek het op die maksimum stroom (JSC) wat die selle produseer: hoe korter die die akiel ketting, hoe hoër die JSC. Hierdie makroskopiese ondersoek is voltooi deur mikroskopiese metings in die vorm van tydopgelosde absorpsiespektroskopie. Dit laat ons toe om die fotogeinduseerde oksidasie asook regenerasie van die kleurstof te volg soos wat dit plaas vind deur gewenste sowel as ongewenste roetes. Dit is bevind dat die inspuitings effektiwiteit van die kleurstof molekules direk verantwoordelik is vir die waarneembare trajek in die kortsluitings stroom.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This study’s focus is on the determination and quantization of radiation damage on a cellular level due to the decay of the Auger electron-emitting 123I and the replication of this energy deposition using Geant4 Monte Carlo simulations. The relatively short half-life of 123I (13.2 hours) makes it ideal for studies of Auger electrons which induce biological damage similar to that of high linear energy transfer radiations, when permitted to deposit their energy in close proximity to DNA. Due to small cellular dimensions, direct dose measurements are impossible but estimates may be made from Monte Carlo simulations. In this investigation the thymidine analogue 5-[123I]-iodo-2-deoxyuridine (123IUdR) was used to incorporate the 123I into the cellular DNA of T-lymphocytes from two human donors. Radiation induced micronuclei were numerated in binucleated cells using fluorescence microscopy. The energy deposition per decay of 123I was calculated within a spherical geometry, having the same size and density as a human lymphocyte, using the open source Geant4 toolkit. The absorbed energy per disintegration was used to convert the incorporated 123I activity (Bq) into absorbed dose (Gy) values, in order to compare the biological damage caused by the radioactive iodine to 60Co γ-radiation. A linear relationship between micronuclei frequency and 123I activity could be established. The linear dose-response noted for Auger electrons in the study is indicative of the high-LET nature of these particles. Using the linear-quadratic dose-response curve for micronuclei frequencies following exposure to graded doses of 60Co γ-rays, the relative biological effectiveness (RBE) of the DNA incorporated 123I estimated in this work was found to range from 19 ± 10 to 32 ± 7 for lymphocyte donor 1 and 15 ± 6 to 42 ± 11 for donor 2. The dose limiting RBE (RBEM) for lymphocyte donor 1 and 2 are respectively 34 ± 8 and 50 ± 15 and follows the expected shift in terms of the inherent radiosensitivity of the donors. We also considered the inclusion of the S-phase fraction of the lymphocytes in the dosimetry calculations. The resultant RBEs of the dose points of lymphocyte donor 1 ranges from 4 ± 2 to 7 ± 2, and those of donor 2 ranges from 3 ± 1 to 9 ± 2. The RBEM for lymphocyte donor 1 and 2 are respectively 7 ± 2 and 11 ± 3. The inclusion of the S-phase fraction reduces the calculated RBEs significantly and these observed RBE values relate well to those obtained in studies with fibroblasts and 125IUdR. / AFRIKAANSE OPSOMMING: Hierdie studie fokus op die bepaling en kwantisering van stralingskade op 'n sellulêre vlak as gevolg van die verval van 123I wat Auger elektrone afgee, asook die simulering van hierdie energie afsetting met behulp van die Geant4 Monte Carlo program. Die relatiewe kort half-leeftyd van 123I (13.2 uur) maak dit ideaal vir studies van Auger elektrone wat biologiese skade soortgelyk aan dié van 'n hoë lineêre-energie-oordrag uitstraling veroorsaak, indien die energie van die elektrone naby sellulêre DNA geabsorbeer word. As gevolg van die klein sellulêre dimensies is direkte dosis metings egter onmoontlik, maar skattings kan gemaak word met behulp van Monte Carlo simulasies. Die timidien analoog 5-[123I]-jodo-2-deoxyuridien (123IUdR) was in hierdie ondersoek gebruik om die 123I in die DNA van menslike T-limfosiete in te bou. Mikrokerne in dubbel-kernige selle wat vorm as gevolg van die Auger elektrone was getel met behulp van fluoressensie mikroskopie. Die energie afsetting per 123I verval was bereken binne ‘n sferiese geometrie, met dieselfde grootte en digtheid as 'n menslike limfosiet, met behulp van die Geant4 sagteware. Die geabsorbeerde energie per verval was gebruik om die geïnkorporeerde 123I aktiwiteit (Bq) om te skakel na ‘n waarde van geabsorbeerde dosis (Gy), ten einde die biologiese skade wat veroorsaak word deur die radioaktiewe jodium-123 met kobalt-60 gamma straling te vergelyk. ‘n Lineêre verwantskap tussen die mikrokerne frekwensies en die 123I aktiwiteit is vasgestel. Hierdie verwantskap vir Auger elektrone is 'n aanduiding van die hoë lineêre-energie-oordrag van hierdie deeltjies. Die lineêr-kwadratiese dosis-effek krommes vir mikrokerne frekwensies na blootstelling aan 60Co γ-strale was gebruik om die relatiewe biologiese doeltreffendheid (RBE) van die DNA geïnkorporeerde 123I te beraam. RBE waardes wissel van 19 ± 10 tot 32 ± 7 vir limfosiete van skenker 1 en 15 ± 6 tot 42 ± 11 vir skenker 2. Die dosis beperkte RBE (RBEM) vir limfosiet skenker 1 en 2 is onderskeidelik 34 ± 8 en 50 ± 15 en volg die verwagte skuif in terme van die inherente radiogevoeligheid van die skenkers. Die fraksie van limfosiete wat in S-fase was tydens die blootstelling aan 125IUdR was ingesluit in verdere dosimetrie berekeninge. Die gevolglike RBEs van die dosispunte van limfosiete van skenker 1 wissel van 4 ± 2 tot 7 ± 2 en dié van skenker 2 wissel van 3 ± 1 tot 9 ± 2. Die RBEM vir limfosiet skenker 1 en 2 is onderskeidelik 7 ± 2 en 11 ± 3. Die insluiting van die S-fase fraksie verminder die berekende RBEs aansienlik en die RBE waardes waargeneem hou goed verband met die wat in studies met fibroblaste en 125IUdR verkry is.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The binary cluster model is used to investigate the properties of exotic structures and decays in various nuclei. A simple method is described to choose the possible clusters forming within the nucleus, by assuming the nucleus consists of a mixture of up to four different core-cluster pairs. A phenomenological potential is then used, with optimized parameters, to describe the even-even 222-232Th nuclei within the binary cluster model, by calculating exotic decay half-lives, reduced electromagnetic transition probabilities, and energy spectra. After finding that all experimentally observed heavy ion emissions are predicted with the model and calculated structure observables are reproduced within good agreement of the experimentally measured values, the model was extended to include the even-even 230-234U, 236-240Pu and 222-224Ra nuclei. We found that almost all experimentally observed heavy ion emissions are predicted within the model with reasonable accuracy in the calculated halflives, and found good agreement in the other calculated structure observables. / AFRIKAANSE OPSOMMING: Die binêre bondel model is gebruik om die eienskappe van eksotiese strukture en verval in verskeie nukliedes te ondersoek. ’n Eenvoudige metode is gebruik om die moontlike bondels wat binne die nuklied vorm te kies, deur die aanname te maak dat die nuklied uit ’n mengsel van tot vier verskillende kern-bondel pare bestaan. ’n Fenomenologiese potensiaal is dan gebruik, met optimale parameters, om die ewe-ewe 222-232Th nukliedes met die binêre bondel model te beskryf, deur eksotiese verval halfleeftye, verminderde elektromagnetiese oorgangswaarskynlikhede, en energie spektra te bereken. Nadat daar gevind is dat alle vrygestelde swaar ione wat eksperimenteel waargeneem is deur die model voorspel word, en berekende struktuur waarneembares tot goeie ooreenstemming met die eksperimentele waardes produseer is, is die model uitgebrei om die ewe-ewe 230-234U, 236-240Pu en 222-224Ra nukliedes in te sluit. Daar is gevind dat byna alle vrygestelde swaar ione wat eksperimenteel waargeneem is deur die model voorspel word met redelike akkuraathied in die berekening van hul halfleeftye, asook dat daar goeie ooreenstemming tussen die berekende en eksperimentele waardes van ander struktuur waarneembares was.

Thesis (PhD (Physics))--Stellenbosch University, 2009. / ENGLISH ABSTRACT: This dissertation investigates certain key aspects of mathematical modeling of HIV and TB epidemics in South Africa with particular emphasis on data from a single well-studied community. Data collected over a period of 15 years (1994 to 2009) in Masiphumelele, a township near Cape Town, South Africa are used to develop a community-level mathematical model of the local HIV-TB epidemic. The population is divided into six compartments and a system of di®erential equations is derived to describe the spread of the dual epidemic. Our numerical results suggest that increased access to antiretroviral therapy (ART) could decrease not only the HIV prevalence, but also the TB noti¯cation rate. We present a modeling framework for studying the statistical properties of °uctuations in models of any population of a similar size. Viewing the epidemic as a jump process, the method entails an expansion of a master equation in a small parameter; in this case in inverse powers of the square root of the population size. We derive two-time correlation functions to study the correlation between di®erent types of active TB events, and show how a temporal element could be added to the de¯nition of TB clusters, which are currently de¯ned solely by DNA type. We add age structure to the HIV-TB model in order to investigate the demographical impact of HIV-TB epidemics. Our analysis suggests that, contrary to general belief, HIV-positive cases are not making a substantial contribution to the spread of TB in Masiphumelele. We develop an age-structured model of the HIV-TB epidemic at a national level in order to study the potential impact of a proposed universal test and treat program for HIV on dual HIV-TB epidemics. Our simulations show that generalized ART could signi¯cantly reduce the TB noti¯cation rate and the TB-related mortality rate in the short term. The timescale of the impact of ART on HIV prevalence is likely to be longer. We study the potential impact of more conventional control measures against HIV. Guidance for possible future and/or additional interventions emerge naturally from the results. We advocate a reduction in intergenerational sex, based on our ¯nding that 1.5-2.5 standard deviation in the age di®erence between sexual partners is necessary to create and sustain a major HIV epidemic. A simulation framework is developed to help quantify variance in age-structured epidemic models. The expansion technique is generalized to derive a Fokker-Planck equation. Directions for future work, particularly in terms of developing methods to model °uctuations and validate mixing assumptions in epidemiological models, are identi¯ed. / AFRIKAANSE OPSOMMING: Hierdie proefskrif ondersoek aspekte van die wiskundige modelering van HIV en TB epi- demies in Suid Afrika en fokus ook op 'n spesi¯eke gemeenskap. Data wat oor 'n periode van 15 jaar ingesamel is (1994 tot 2009) in Masiphumelele, 'n woonbuurt naby Kaapstad, Suid Afrika word gebruik om 'n wiskundige model te skep wat HIV-TB in die gemeen- skap modeleer. Die populasie word in ses kompartemente verdeel en 'n stel di®erensiaal vergelykings word afgelei om die verspreiding van di¶e epidemies te ondersoek. Ons nu- meriese resultate toon aan dat verhoogde toegang tot antiretrovirale behandeling (ARB) die potensiaal het om HIV prevalensie die TB koers beduidend te laat daal. Ons ontwikkel 'n raamwerk waarmee die statistiese eienskappe van °uktuasies ondersoek kan word in enige populasie van dieselfde grootte. Die metode ontwikkel 'n meester vergelyking vir die on- derliggende geboorte-dood stogastiese proses en brei dit uit in terme van 'n klein parameter; in di¶e geval in inverse magte van die vierkantswortel van die populasie grootte. Die twee-tyd korrelasie funksies word afgelei, en word gebruik om die korrelasie tussen verskillende tipes van TB episodes te bestudeer, asook om te wys hoe 'n tydselement aan die de¯nisie van TB groeperings gegee kan word. Di¶e word tans slegs d.m.v DNA tipe geklassi¯seer. Ouderdom- struktuur word aan die model toegevoeg om die demogra¯ese impak van HIV-TB epidemies te bestudeer. Ons analise toon aan dat, anders as wat algemeen aanvaar word, maak HIV- positiewe gevalle nie 'n groot bydrae tot die verspreiding van TB in Masiphumelele nie. Ons ontwikkel 'n ouderdom-gestruktureerde model van HIV-TB op nasionale vlak en gebruik die model om die potensiÄele impak van 'n universele toets- en behandel strategie op die HIV-TB epidemies te ondersoek. Ons simulasies toon aan dat algemene ARB waarskynlik 'n groot impak op die TB aanmeldings koers asook die TB-verwante mortaliteits koers kan h^e binne 'n relatiewe kort tydperk. Die impak op HIV prevalensie sal eers oor 'n veel langer periode duidelik word. Ons ondersoek ook die moontlikheid van meer konvensionele beheermaa- treels. Ons ontmoedig tussengenerasie seksuale omgang, gegrond op ons bevinding dat 'n standaard afwyking van 1.5-2.5 in die ouderdoms verskil tussen seksuele vennote, nodig is om 'n HIV epidemie van stapel te stuur en te onderhou. Ons ontwikkel 'n simulasie raamwerk om variansie in ouderdomgestruktureerde modelle te benader. Die uitbreidingstegniek word veralgemeen om 'n Fokker-Planck vergelyking af te lei. Ons identi¯seer probleme in die on- twikkeling van metodes om interaksie patrone en °uktuasies te modeleer in epidemiologiese modelle as opgawe vir toekomstige werk.

Thesis (PhD (Physics))--Stellenbosch University, 2008. / The advent of high intensity short pulse lasers has opened the door to investigating buried solid-solid interfaces through the technique of optical second harmonic generation (SHG). This has led to extensive study of technologically important systems such as the Si/SiO2 interface. In this study, SHG is employed to study the interface between highly boron doped p+-type Si and its native oxide layer (SiO2). Previous studies from this laboratory have extensively investigated the photo-induced charge transfer process across the Si/SiO2 interface in the case of undoped natively oxidized Si by means of SHG, with initial SHG measurements being performed on boron doped p+-type Si. The natively oxidized p+-type Si/SiO2 sample was placed on a computer controlled positioning system which allowed for translation of the sample and rotation around the azimuth. The laser system employed was characterized in terms of spectral composition, pulse duration, pulse repetition rate, spatial pro le and pulse energy in order to ensure quantitative measurements. The SHG signal generated from the sample interface was recorded in re ection. Under the applied irradiation conditions, defects are created at the interface by the near infra red (NIR) femtosecond radiation from the laser. These defects are then populated via multi-photon processes by electrons and to a lesser extent holes. The charge transfer across the interface induces an interfacial electric eld. This photo-induced electric eld is in addition to the built-in interfacial electric eld caused by positive ionization of naturally occurring interfacial defects due to the strong doping of the bulk Si. It is this interfacial electric eld, consisting of the built-in doping induced eld and the photo-induced electron and hole elds, that is probed by SHG. The SHG signal is strongly dependent on the magnitude of this interfacial electric eld as the electric eld induced second harmonic (EFISH) signal dominates all other contributions to the observed SHG signal in the case of the Si/SiO2 system. The temporal evolution of the SHG signal is recorded for di erent intensities from virgin as well as the pre-irradiated samples. This yields information about the time scales on which the charge separation occurs as well as the in- uence of existing photo-induced trap sites on the charge separation process, since the strength of the SHG signal is an indirect measure of the interfacial electric eld strength. The angular dependence of the SHG signal (SH rotational anisotropy measurements) for both the initial signal (when the doping induced electric eld dominates) and the saturated signal (when the electron induced electric eld dominates) is measured. Both these measurements show a four fold symmetry but with a relative 45 phase shift between them. This iii is taken as con rmation of the reversal of the interfacial electric eld direction. The initial SHG signal as a function of intensity is also recorded for di erent incident wavelengths. The variation in the non-quadratic dependence of the initial SHG signal on the incident intensity is attributed to a resonant enhancement of two-photon absorption and subsequent screening of the interfacial electric eld by charge carriers. The measurement performed and the results obtained contribute to the understanding of the photo-induced charge separation process across buried solid-solid interfaces, speci cally as it applies to the important Si/SiO2 interface.

Thesis (PhD (Physics))-University of Stellenbosch, 2009. / ENGLISH ABSTRACT: A binary cluster model is used to investigate the properties of the ground state band of 212Po, modelled as a 208Pb-alpha core-cluster system. The results obtained using a microscopic corecluster potential are compared to those obtained with a purely phenomenological potential. The two potentials were found to exhibit similar surface behaviour and thus give similar predictions for the ground state alpha decay half-life. They however generate very different energy spectra, with the results from the phenomenological potential clearly superior. We optimize the phenomenological potential parameters, and propose an additional short range interaction to improve the underbinding generally found for the J¼ = 0+ ground state. We then investigate two possible scenarios for generating the negative parity states in 212Po. We find that both are necessary in order to produce low-lying negative parity states which are able to decay via electric dipole transitions to the positive parity states of the ground state band. Finally we present a novel calculation of the properties of the low-lying positive and negative parity states of 218Rn described as a doubly closed 208Pb core plus a 10Be cluster. / AFRIKAANSE OPSOMMING: ’n Binêre bondel model word gebruik om die eienskappe van die grondtoestands energie band van 212Po, te modeleer as ’n 208Pb-alpha kern-bondel sisteem te ondersoek. Die resultate verkry vanaf ’n mikroskopiese kern-bondel potentiaal word vergelyk met die wat verkry is met ’n suiwer fenomenologiese potentiaal. Die twee potentiale is verkry om dieselfde oppervlakte toestande voor te stel en gee sodoende dieselfde voorspellings vir die grondtoestand alpha verval halfleeftyd. Alhoewel dit baie verskillende energie spektra genereer, toon die resultate van die fenomenologiese potentiaal dat dit duidelik beter is. Ons optimiseer hierdie fenomenologiese parameters en stel ’n addisionele kort ry-afstands interaksie voor om die algemene ondergebondenheid wat oor die algemeen by die J¼ = 0+ grondtoestand voorkom, te verbeter. Ons ondersoek ook hierdie twee moontlike scenarios om die negatiewe pariteitstoestande in 212Po te genereer. Ons vind dat beide scenarios noodsaaklik is om laagliggende pariteitstoestande te produseer, sodat verval deur elektriese dipool oorgange na die positiewe pariteitstoestande van die grondtoestandsband moontlik is. Laagliggende positiewe en negatiewe pariteitstoestande, van die 218Rn wat beskryf word as ’n dubbelgeslote 208Pb kern en ’n 10Be bondel.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The generation of ultrafast light pulses and the development of time resolved spectroscopic techniques, such as the femtosecond pump probe spectroscopy technique, have facilitated the study of ultrafast energy transfer in the photosynthetic systems of green plants and photodynamic therapy drugs. It has allowed the investigation of biological and chemical processes that take place on the ultrafast timescale and has allowed us to obtain spectral and kinetic information on energy transfer. In addition, it has allowed time resolved experiments in which the transient absorption of species under investigation was observed and has elucidated molecular dynamics. In the present work this was done with a temporal resolution of approximately 200 fs and covering a pump-to-probe delay range of 300 fs to 2 ns. The main aims of this study were to characterise the femtosecond pump probe spectroscopy system, to investigate the energy transfer in the natural light harvesting complex II (LHC II) in view of future expansion to the study of synthesized arti cial functional light harvesting complexes and nally to study ultrafast processes in zinc phthalocyanine (ZnPc) systems. In photosynthetic organisms, LHC II is the most abundant light harvesting complex and it plays an important role in light harvesting and photoprotection. The light energy is absorbed by light harvesting complexes and transferred to a reaction centre (RC) in an ultrafast timescale. Phthalocyanines are a new class of photosensitiser used for photodynamic therapy. These drugs are used to treat small and super cial tumours. The energy transfer from the singlet excited state to the triplet excited state occurs on an ultrafast timescale. However, recent work done on zinc phthalocyanine has proved that the determination of the ultrafast component remains a challenge. Several ultrafast studies carried out on ZnPc in solvents have been not only unsuccessful to give a clear picture of the ultrafast dynamics but have also produced divergent results. In this study, a characterisation of the femtosecond pump probe spectroscopy setup was done. The samples under investigation were probed by a white light continuum. The generation of the white light continuum introduced chirp, which in uenced the temporal evolution of the transient absorption results. The technique used to correct the chirp introduced by white light generation is discussed in detail. Our femtosecond pump probe spectroscopy setup was benchmarked by using a well known dye, namely malachite green. In addition, the investigation of the transient absorption change of LHC II, an active component in photosynthesis, as extracted from spinach leaves and the ultrafast dynamics of a promising photosensitiser ZnPc in dimethyl sulfoxide (DMSO) as well as in dimethyl formamide (DMF) was done. The spectral and dynamic results obtained using these three samples are described and exponential ts to the absorbance decay curves used to estimate the timescales of the energy transfer processes are presented. In this experiment, the dynamics and measured time constants related to the energy transfer between the different types of chlorophyll in LHC II was monitored, whereas with ZnPc, the dynamics and the measured time constants associated with solvation dynamics and vibrational relaxation was examined. / AFRIKAANSE OPSOMMING: Die vorming van ultravinnige lig pulse en die ontwikkeling van tyd opgelosde spektroskopiese tegnieke, soos die femtosekonde pomp proef spektroskopie tegniek, het die studie van ultravinnige energie oordrag in fotosintetiese stelsels van groen plante en chemiese prosesse gefasiliteer, wat kan plaasvind op die ultravinnige tyd skaal en laat dit toe om spektrale en kinetiese informasie oor die energie oordrag te kan bepaal. Dit het ook dit moontlik gemaak om tyd opgelosde eksperimente te kan doen waarin ons veranderlike absorbsie van die monster kon ondersoek en die molekulere dinamika kon ontrafel. In hierdie werk is dit gedoen met n tyd resolusie van omtrent 200 fs termyl 'n pomp-tot-proef tydvertraging van 300 fs tot 2 ns gebruik is. Die hoof doelwitte van hierdie werk was om 'n femtosekonde pomp proef spektroskopie stelsel te karakteriseer, die energie oordrag in die natuurlike ligoes kompleks II te ondersoek met die toekomstige uitbreiding van die studie na sintetiese lig-oes komplekse as oogmerk en laastens om ultravinnige prosesse in Sink Ftalosianiene stelsels te ondersoek. In fotosintetiese organismes, is lig oes kompleks II die mees volop lig oes kompleks en speel 'n belangrike rol in lig oes en foto skerming. Die lig energie word geabsorbeer deur lig oes komplekse en dan oorgedra na reaksie middelpunte in 'n ultravinnige tydskaal. Ftalosianiene is 'n nuwe klas fotosensiteerder wat gebruik word in fotodinamiese terapie. Hierdie dwelms word gebruik om klein en oppervlakkige gewasse te behandel. Die energie oordrag van die opgewekte singlet tot die triplet toestand vind plaas op die ultravinnige tydskaal. Onlangse navorsingswerke het getoon dat die bepaling van die ultravinnige komponent 'n uitdaging bly. Verskeie vorige ondersoeke is gedoen op Sink Ftalosianiene in verskeie oplosmiddels, en nie net het hierdie studies nie 'n helder prentjie verskaf van die ultravinnige dinamika nie, maar het ook divergerende resultate opgelewer. In hierdie werk word 'n karakterisering van die femtosekonde pomp proef spektroskopie stelsel gedoen. Die monsters is ondersoek met 'n wit lig kontinuum proef. Die vorming van die wit lig kontinuum het tjirp veroorsaak, wat die tyd evolusie van die veranderlike absorbsie resultate beinvloed het. Die tegniek wat gebruik was om die tjirp te korregeer word bespreek. Ons femtosekonde pomp proef spektroskopie stelsel is gestandardiseer deur die welbekende kleurstof malachiet groen. Ons het ook die veranderlike absorbsie van lig oes kompleks II ondersoek, 'n aktiewe komponent in fotosintese, soos dit onttrek is uit spinasie blare, asook die ultravinnige dinamika van die belowende photosensitizer Sink Ftalosianiene in DMSO asook DMF. Die spektrale en dinamiese resultate verkry vanaf hierdie drie monsters word beskryf en eksponensiele passings aan die absorbsie verval kurwes is gebruik om die tydskale van die energie oordrag prosesse te skat. In hierdie eksperiment is dinamika en gemete tydkonstantes waargeneem wat toegeskryf kan word aan die energie oordrag tussen verskillende soorte chloro l in lig oes kompleks II. In die Sink Ftalosianien eksperimente is dinamika en gemete tydkonstantes waargeneem wat toegeskryf kan word aan solverings dinamika asook vibrasionele ontspanning.