The main aim of this thesis was to study the role of the indirect actions of γ-rays and α-particles on the complexity of primary DNA damages and the repair fidelity of major DNA repair pathways: non-homologous end joining (NHEJ), homologous recombination repair (HRR) and base excision repair (BER). The complexity of radiation-induced damages increases and the proximity between damages decreases with increasing LET due to formation of ionization clusters along the particle track. The complexity of damages formed can be modified by the free radical scavenger dimethyl sulfoxide (DMSO). In addition, the effects of low doses of low dose rate γ-radiation on cellular response in terms of differentiation were investigated. Paper I investigates the role of the indirect effect of radiation on repair fidelity of HRR, NHEJ and BER when damages of different complexity were induced by radiation or by potassium bromate. We found that potassium bromate induces complex DNA damages through processing of base modifications and that the indirect effect of radiation has a high impact on the NHEJ pathway. Results in paper II confirmed our conclusions in paper I that the indirect effect from both γ-rays and α-particles has an impact on all three repair pathways studied and NHEJ benefits the most when the indirect effect of radiation is removed. In paper III we investigated the effects of low dose/dose rate γ-radiation on the developmental process of neural cells by using cell models for neurons and astrocytes. Our results suggest that low dose/dose rate γ-radiation attenuates differentiation and down-regulates proteins involved in the differentiation process of neural cells by an epigenetic rather than cytotoxic mechanism. / <p>At the time of doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.</p>

The indirect effect of aerosols expresses how changes in aerosols would influence clouds and cause impacts on Earth's climate and hydrological cycle. The current assessment of the interactions between aerosols and clouds is uncertain and parameterizations used to represent cloud processes are not well constrained. This thesis first evaluates a cloud activation parameterization by investigating cloud droplet number concentration closure for stratocumulus clouds sampled during the 2005 MArine Stratus Experiment (MASE). Further analysis of the droplet size distribution characteristics using the extended parameterization is performed by comparing the predicted droplet spectra with the observed ones. The effect of dynamical variability on the droplet size distribution evolution is also investigated by considering a probability density function for updraft velocity. The cumulus and stratocumulus cloud datasets from in-situ field measurements of NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE) and Coastal STRatocumulus Imposed Perturbation Experiment (CSTRIPE) campaigns are used for this task. Using the same datasets, the autoconversion rate is calculated based on direct integration of kinematic collection equation (KCE). Six autoconversion parameterizations are evaluated and the effect of turbulence on magnifying collection process is also considered. Finally, a general circulation model (GCM) is used for studying the effect of different autoconversion parameterizations on indirect forcing estimates. The autoconversion rate given by direct KCE integration is also included by implementing a look-up table for collection kernels. Although these studies add more variability to the current estimate of aerosol indirect forcing, they also provide direction towards a more accurate assessment for climate prediction.

abstract: Time-to-event analysis or equivalently, survival analysis deals with two variables simultaneously: when (time information) an event occurs and whether an event occurrence is observed or not during the observation period (censoring information). In behavioral and social sciences, the event of interest usually does not lead to a terminal state such as death. Other outcomes after the event can be collected and thus, the survival variable can be considered as a predictor as well as an outcome in a study. One example of a case where the survival variable serves as a predictor as well as an outcome is a survival-mediator model. In a single survival-mediator model an independent variable, X predicts a survival variable, M which in turn, predicts a continuous outcome, Y. The survival-mediator model consists of two regression equations: X predicting M (M-regression), and M and X simultaneously predicting Y (Y-regression). To estimate the regression coefficients of the survival-mediator model, Cox regression is used for the M-regression. Ordinary least squares regression is used for the Y-regression using complete case analysis assuming censored data in M are missing completely at random so that the Y-regression is unbiased. In this dissertation research, different measures for the indirect effect were proposed and a simulation study was conducted to compare performance of different indirect effect test methods. Bias-corrected bootstrapping produced high Type I error rates as well as low parameter coverage rates in some conditions. In contrast, the Sobel test produced low Type I error rates as well as high parameter coverage rates in some conditions. The bootstrap of the natural indirect effect produced low Type I error and low statistical power when the censoring proportion was non-zero. Percentile bootstrapping, distribution of the product and the joint-significance test showed best performance. Statistical analysis of the survival-mediator model is discussed. Two indirect effect measures, the ab-product and the natural indirect effect are compared and discussed. Limitations and future directions of the simulation study are discussed. Last, interpretation of the survival-mediator model for a made-up empirical data set is provided to clarify the meaning of the quantities in the survival-mediator model. / Dissertation/Thesis / Doctoral Dissertation Psychology 2017

South Africans are engaged in daily battles with work-related and non-work related issues. Although an organisation is not capable of addressing or changing all the issues experienced by the South African population, it can intervene in order to improve the quality of its employees’ working lives. A suggested starting point is person-environment fit (PE fit), due to its effect on job satisfaction and intentions to leave. Consequently, when an individual experiences low PE fit, it will contribute to job dissatisfaction, and intentions to leave as international research has shown. To possibly decrease the impact of these relationships, it is important for leader empowering behaviour to be evident throughout the organisation. The objectives of this study were to determine possible relationships, indirect effects, and moderating effects between PE fit, job satisfaction, intentions to leave, and leader empowering behaviour. A convenience sample of employees working under the guidance of a leader/manager/supervisor was taken from a retail company in Gauteng. Participation in the study was voluntary. A measuring battery measuring PE fit (i.e. person-organisation fit, needs-supplies fit, and demands-abilities fit), job satisfaction, intentions to leave, and leader empowering behaviour (i.e. delegation of authority, accountability, self-directed decision making, information sharing, skills development, and coaching for innovative performance) was used. Descriptive and inferential statistics, Raykov’s rho coefficients, Pearson product-moment correlations, measurement models, structural models, and goodness-of-fit statistics were used to analyse the data. The results indicate that PE fit has a positive relationship with job satisfaction. Job satisfaction has a negative relationship with intentions to leave. PE fit has an indirect effect on intentions to leave via job satisfaction. Leader empowering behaviour moderates the relationship between job satisfaction and intentions to leave. Various recommendations were made for the selected retail company as well as for future research. The retail company and employees should comprehend the impact of PE fit on outcomes such as job satisfaction and intentions to leave, as both parties are equally affected by its implications. Therefore, both pro-active and re-active measures should be institutionalised to address PE fit. Additionally, the retail company should understand the importance of leader empowering behaviour and the impact it can have on their business unit and the organisation as a whole. Recommendations for future research include longitudinal research designs, as well as the expansion of research beyond the selected company in the retail industry. / MCom (Industrial Psychology)--North-West University, Vaal Triangle Campus, 2015

South Africans are engaged in daily battles with work-related and non-work related issues. Although an organisation is not capable of addressing or changing all the issues experienced by the South African population, it can intervene in order to improve the quality of its employees’ working lives. A suggested starting point is person-environment fit (PE fit), due to its effect on job satisfaction and intentions to leave. Consequently, when an individual experiences low PE fit, it will contribute to job dissatisfaction, and intentions to leave as international research has shown. To possibly decrease the impact of these relationships, it is important for leader empowering behaviour to be evident throughout the organisation. The objectives of this study were to determine possible relationships, indirect effects, and moderating effects between PE fit, job satisfaction, intentions to leave, and leader empowering behaviour. A convenience sample of employees working under the guidance of a leader/manager/supervisor was taken from a retail company in Gauteng. Participation in the study was voluntary. A measuring battery measuring PE fit (i.e. person-organisation fit, needs-supplies fit, and demands-abilities fit), job satisfaction, intentions to leave, and leader empowering behaviour (i.e. delegation of authority, accountability, self-directed decision making, information sharing, skills development, and coaching for innovative performance) was used. Descriptive and inferential statistics, Raykov’s rho coefficients, Pearson product-moment correlations, measurement models, structural models, and goodness-of-fit statistics were used to analyse the data. The results indicate that PE fit has a positive relationship with job satisfaction. Job satisfaction has a negative relationship with intentions to leave. PE fit has an indirect effect on intentions to leave via job satisfaction. Leader empowering behaviour moderates the relationship between job satisfaction and intentions to leave. Various recommendations were made for the selected retail company as well as for future research. The retail company and employees should comprehend the impact of PE fit on outcomes such as job satisfaction and intentions to leave, as both parties are equally affected by its implications. Therefore, both pro-active and re-active measures should be institutionalised to address PE fit. Additionally, the retail company should understand the importance of leader empowering behaviour and the impact it can have on their business unit and the organisation as a whole. Recommendations for future research include longitudinal research designs, as well as the expansion of research beyond the selected company in the retail industry. / MCom (Industrial Psychology)--North-West University, Vaal Triangle Campus, 2015

O presente trabalho apresenta a aplicação das fórmulas de Vincenty nos cálculos das correções do terreno e do efeito indireto, que desempenham papel relevante na construção de cartas geoidais. Implementa-se um programa de processamento que realiza a integração numérica sobre o modelo digital do terreno, discretizado em células triangulares de Delaunay. O sistema foi desenvolvido com a linguagem de programação FORTRAN, para a execução de intensos algoritmos numéricos usando compiladores livres e robustos. Para o cálculo do efeito indireto, considera-se a redução gravimétrica efetuada com base no segundo método de condensação de Helmert, face ao pequeno valor de efeito indireto no cálculo do geóide, em função da mudança que este produz no potencial da gravidade devido ao deslocamento da massa topográfica. Utiliza-se, o sistema geodésico SIRGAS 2000 como sistema de referência para o cômputo das correções. Simplificando o exame dos resultados alcançados, distingue-se o processamento e desenvolvimento do trabalho em etapas como a escolha de ferramentas geodésicas para máxima precisão dos resultados, elaboração de subrotinas e comparação de resultados com cálculos anteriores. Os resultados encontrados foram de geração sadia e satisfatória e podem ser perfeitamente empregados no cálculo do geóide em qualquer área do globo. / An application of Vincentys formulas has been presented for computing terrain corrections and indirect effect, that have important hole in geoidal maps generation. A software is implemented, that performs numerical integration over a digital terrain model discretized in Delaunay triangular cells. The system had been implemented in FORTRAN Programming Language, as a natural choice for implementation of intensive numerical algorithms, using free and robust compilers. To calculate the indirect effect is used the gravimetric reductions, based on Helmert Second Condensation Method, because of small indirect effect values in calculation of the geoid, depending on the gravity potential change due to displacement of topographical masses. The Geodetic System SIRGAS 2000 is adopted as the reference system to compute the corrections. Simplifying the analysis of the obtained results, the processing and development of the study in stages like choice of geodetic tools for maximum accuracy of results, preparation of subroutines and compare results with previous calculations. The results observed were sound satisfactory and support conveniently geoid generation in any part of globe.

The aerosol direct and indirect effects were investigated for three specific cases during the March 2000 Cloud IOP at the SGP site by using a modified WRF model. The WRF model was previously altered to include a two-moment bulk microphysical scheme for the aerosol indirect effect and a modified Goddard shortwave radiation scheme for the aerosol direct effect. The three cases studied include a developing low pressure system, a low precipitation event of mainly cirrus clouds, and a cold frontal passage. Three different aerosol profiles were used with surface concentrations ranging from 210 cm-3 to 12,000 cm-3. In addition, each case and each aerosol profile was run both with and without the aerosol direct effect. Regardless of the case, increasing the aerosol concentration generally increased cloud water and droplet values while decreasing rain water and droplet values. Increased aerosols also decreased the surface shortwave radiative flux for every case; which was greatest when the aerosol direct effect was included. For convective periods during polluted model runs, the aerosol direct effect lowered the surface temperature and reduced convection leading to a lower cloud fraction. During most convective periods, the changes to cloud, rain, and ice water mixing ratios and number concentrations produced a nonlinear precipitation trend. A balance between these values was achieved for moderate aerosol profiles, which produced the highest convective precipitation rates. In non-convective cases, due to the presence of ice particles, aerosol concentration and precipitation amounts were positively correlated. The aerosol threshold between precipitation enhancement and suppression should be further studied for specific cloud types as well as for specific synoptic weather patterns to determine its precise values.

<p>This dissertation presents the first findings of aerosol indirect effect in the foothills of the Himalayas (Central Nepal), through a systematic research approach involving satellite data analysis, field campaign, growth factor estimation and numerical modeling studies. Satellite retrieved aerosol optical depth data over the region were first used to identify the dominant modes of spatial/temporal variability of aerosols in the region. Based on the observed dominant spatial mode of aerosol in the pre-monsoon season (Shrestha and Barros 2010, ACP), a field campaign was organized under the Joint Aerosol Monsoon Experiment (JAMEX09) at Dhulikhel and Besisahar to simultaneously measure dry and ambient aerosols size spectra using SMPS and chemical composition using filters (Shrestha et al. 2010, ACP). The diurnal cycle of aerosol number concentration exhibited a consistent peak in the morning and evening period, which was found to be associated with increase in local emission and the delay in ventilation of aerosol through upslope flows and mixing (inferred from an idealized numerical study over Besisahar). The aerosol size distribution was mostly unimodal at night and bimodal during the day, with a consistent larger mode around 100nm and a smaller mode located around 20nm. The chemical composition of PM2.5 was dominated by organic matter at both sites. Organic carbon (OC) comprised the major fraction (64~68%) of the aerosol concentration followed by ionic species (24~26%, mainly and ). Elemental Carbon (EC) compromised 7~10% of the total composition and 27% of OC was found to be water soluble at both sites. The aerosol number concentration increased and decreased in the presence of synoptic scale aerosol plumes and after rainfall events respectively.</p><p>A simple model based on Köhler theory was used to explain the observed growth factor using an assumption of (NH4)2SO4 aqueous solution including the presence of slightly soluble organic compounds (SSC) with an insoluble core as a function of molality and mass-fraction. The measured growth factors suggest that the aerosols are in metastable state due to the strong diurnal cycle of relative humidity (RH). The bulk hygroscopic parameter estimated from the DGF and chemical composition of aerosols suggests less hygroscopic aerosols at both locations as compared to previous studies. The dry aerosol size distribution and the bulk hygroscopic parameters were used to estimate the cloud condensation nuclei (CCN) spectrum, which was vertically scaled up to lifting condensation level (LCL) assuming that the shape and chemical properties of aerosol remains unchanged (Shrestha et al. 2011, submitted to JGR). Finally, these regional CCN spectra for polluted and clean conditions as well as standard continental and marine spectra used in numerical weather prediction models (Cohard et al. 1998) were used to probe CCN sensitivity for a pre-monsoon storm system in Central Nepal during JAMEX09. A significant shift in the maxima of the accumulated precipitation was observed between the continental aerosol spectra (Cohard et al. 1998) and the polluted spectra for Dhulikhel. This shift caused the displacement of rainfall maximum away from the Kulekhani water reserve catchment, which is key to hydropower in Nepal. Detailed analysis of the simulations suggests that simgnificant differences in the space-time variability and intensity of precipitation, if not areally integrated amounts, can be explained by differences in the timing and intensity of latent heat release and absorption due to freezing/melting of hydrometers and evaporative cooling of droplets, strengthening cold pool formation and associated circulations. This numerical study provides the first look on the aerosol indirect effect over Nepal for a single pre-monsoon rainfall event, and how aerosols can potentially affect the precipitation distribution (to be submitted to JGR). In addition, it shows the importance of using regionally consistent CCN spectra in model parameterizations of aerosol-cloud interactions. At local places, the differences in simulated precipitation between marine, JAMEX09 clean and polluted air spectra were smaller (up tp ± 50%) than the difference between those simulations and the standard continental aerosol spectra (±200%).</p> / Dissertation

An aerosol module is developed and coupled to a regional climate model to investigate the direct and indirect effect of anthropogenic aerosols (sulfate and carbonaceous aerosols) on climate with a focus on precipitation over East Asia. This fully coupled regional climate-chemistry-aerosol model is capable of understanding the interactions between the aerosol perturbation and climate change. The simulated aerosol spatial and seasonal distributions are generally consistent with the observations. The magnitude of the simulated total aerosol concentration and optical depth is about 2/3 of the observed value, suggesting the estimated climatic effects in this work are reasonable and conservative. With the implementation of various aerosol effect, i.e., direct, semi-direct, 1st and 2nd indirect effect, the aerosols?impacts on climate are assessed over the region. The direct, semi-direct and 1st indirect effects generate a negative surface solar forcing, leading to a surface cooling, and the semi-direct effect also heats the atmosphere by BC absorption. This, in turn, increases the atmospheric stability and tends to inhibit the precipitation. The precipitation reduction is largest in the fall and winter, up to -10% with the inclusion of both direct and 1st indirect effects. The 2nd indirect effect using BH94 scheme produces a comparable magnitude in long-wave heating as the solar cooling, leading to the nighttime temperature warming of 0.5K, and a reduction in the diurnal temperature range. The precipitation reduction from the 2nd indirect effect strongly depends on the auto-conversion scheme, with about -30% in the fall and winter, and -15% in the spring and summer using BH94 scheme, while less than -5% using TC80 scheme. By allowing the feedbacks between aerosols and climate, the coupled model generally decreases the discrepancies between the model-simulated and observed precipitation and aerosols over the region. The EOF analysis of the climatological precipitation from last century over East Asia shows a decreasing mode in the EOF leading modes in the fall and winter, and is generally geographically consistent with the distribution of the model simulated precipitation reduction from anthropogenic aerosols.

The Second Aerosol Characterization Experiment (ACE-2) data set along with ECMWF reanalysis meteorological fields provided the basis for the single column model (SCM) simulations, performed as part of the PACE (Parameterization of the Aerosol Indirect Climatic Effect) project. Six different SCMs were used to simulate ACE-2 case studies of clean and polluted cloudy boundary layers, with the objective being to identify limitations of the aerosol/cloud/radiation interaction schemes within the range of uncertainty in in situ, reanalysis and satellite retrieved data. The exercise proceeds in three steps. First, SCMs are configured with the same fine vertical resolution as the ACE-2 in situ data base to evaluate the numerical schemes for prediction of aerosol activation, radiative transfer and precipitation formation. Second, the same test is performed at the coarser vertical resolution of GCMs to evaluate its impact on the performance of the parameterizations. Finally, SCMs are run for a 24–48 hr period to examine predictions of boundary layer clouds when initialized with large-scale meteorological fields. Several schemes were tested for the prediction of cloud droplet number concentration (N). Physically based activation schemes using vertical velocity show noticeable discrepancies compared to empirical schemes due to biases in the diagnosed cloud base vertical velocity. Prognostic schemes exhibit a larger variability than the diagnostic ones, due to a coupling between aerosol activation and drizzle scavenging in the calculation of N. When SCMs are initialized at a fine vertical resolution with locally observed vertical profiles of liquid water, predicted optical properties are comparable to observations. Predictions however degrade at coarser vertical resolution and are more sensitive to the mean liquid water path than to its spatial heterogeneity. Predicted precipitation fluxes are severely underestimated and improve when accounting for sub-grid liquid water variability. Results from the 24–48 hr runs suggest that most models have problems in simulating boundary layer cloud morphology, since the large-scale initialization fields do not accurately reproduce observed meteorological conditions. As a result, models significantly overestimate optical properties. Improved cloud morphologies were obtained for models with subgrid inversions and subgrid cloud thickness schemes. This may be a result of representing subgrid scale effects though we do not rule out the possibility that better large-forcing data may also improve cloud morphology predictions.