Browsing by Subject "simulation"

Now showing 1 - 11 of 11
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    Case study: Custom-designed virtual experiment in fracture mechanics in Mechanical Engineering
    (2008-11-30) Hodgkinson-Williams, Cheryl
    This case study describes the development and use of a custom-designed virtual experiment in Mechanical Engineering which partially simulates the concept of metal fatigue to help student engage with a complex practical application. It then explores some of the enabling or constraining structures, policies and practices at a national, institutional and personal level that appear to have an impact on making such a simulation available as an open educational resource.
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    Decision support for Foodbank South Africa
    (Operations Research Society of South Africa, 2014) Watson, N M; Stewart, T J; Scott, L
    This paper employs a combined 'soft-hard' OR approach to aid decision making in the area of allocation at a not-for-profit organization, Foodbank South Africa (FBSA), that represents the largest hunger-relief network in South Africa. Two problem-structuring tools, causal mapping and root definitions (RDs) are utilized. Causal mapping is used to identify areas for useful research within FBSA, and gain a greater understanding of the organization in terms of its goals and consequently a good appreciation of the context in which decisions are made. Root definitions are employed to acquire a better understanding of the 'decision-issues' within the allocation system at the Cape Town warehouse. A simulation model is developed to imitate daily allocation decisions, with the end-objective of assisting decision-making by developing a range of allocation policies. A decision support system (DSS) is developed to help FBSA manage their agency database, automate some of the daily allocation decisions and simulate allocation policies.
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    DEGREE OF POLARIZATION AND SOURCE COUNTS OF FAINT RADIO SOURCES FROM STACKING POLARIZED INTENSITY
    (2014) Stil, J M; Keller, B W; George, S J; Taylor, A R
    We present stacking polarized intensity as a means to study the polarization of sources that are too faint to be detected individually in surveys of polarized radio sources. Stacking offers not only high sensitivity to the median signal of a class of radio sources, but also avoids a detection threshold in polarized intensity, and therefore an arbitrary exclusion of source with a low percentage of polarization. Correction for polarization bias is done through a Monte Carlo analysis and tested on a simulated survey. We show that the non-linear relation between the real polarized signal and the detected signal requires knowledge of the shape of the distribution of fractional polarization, which we constrain using the ratio of the upper quartile to the lower quartile of the distribution of stacked polarized intensities. Stacking polarized intensity for NVSS sources down to the detection limit in Stokes I, we find a gradual increase in median fractional polarization that is consistent with a trend that was noticed before for bright NVSS sources, but is much more gradual than found by previous deep surveys of radio polarization. Consequently, the polarized radio source counts derived from our stacking experiment predict fewer polarized radio sources for future surveys with the Square Kilometre Array and its pathfinders.
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    Gyromagnetic factors and atomic clock constraints on the variation of fundamental constants
    (2011) Luo, Feng; Olive, Keith A; Uzan, Jean-Philippe
    We consider the effect of the coupled variations of fundamental constants on the nucleon magnetic moment. The nucleon g-factor enters into the interpretation of the measurements of variations in the fine-structure constant, alpha, in both the laboratory (through atomic clock measurements) and in astrophysical systems (e.g. through measurements of the 21 cm transitions). A null result can be translated into a limit on the variation of a set of fundamental constants, that is usually reduced to alpha. However, in specific models, particularly unification models, changes in alpha are always accompanied by corresponding changes in other fundamental quantities such as the QCD scale, Lambda_QCD. This work tracks the changes in the nucleon g-factors induced from changes in Lambda_QCD and the light quark masses. In principle, these coupled variations can improve the bounds on the variation of alpha by an order of magnitude from existing atomic clock and astrophysical measurements. Unfortunately, the calculation of the dependence of g-factors on fundamental parameters is notoriously model-dependent.
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    Mistress Serendipity's Library
    (2014-08-28) d'Angelo, Alex
    Steer Mistress Serendipity on her broom to connect to top-quality free e-resources, useful for high schools and colleges. This game has been designed to help high-school and college students discover top-quality web resources in a fun and exciting way. To use this resource: download the zip file, Extract all in the zip file and click on 'HagLib' to launch the game. This resource was updated on 12 January 2015.
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    PHOTOMETRIC ESTIMATES OF REDSHIFTS AND DISTANCE MODULI FOR TYPE Ia SUPERNOVAE
    (2010) Kessler, Richard; Cinabro, David; Bassett, Bruce; Dilday, Benjamin; Frieman, Joshua A; Garnavich, Peter M; Jha, Saurabh; Marriner, John; Nichol, Robert C; Sako, Masao; Smith, Mathew; Bernstein, Joseph P; Bizyaev, Dmitry; Goobar, Ariel; Kuhlmann, Stephen; Schneider, Donald P; Stritzinger, Maximilian
    Large planned photometric surveys will discover hundreds of thousands of supernovae (SNe), outstripping the resources available for spectroscopic follow-up and necessitating the development of pure ...
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    SASS: South African Simulation Survey a review of simulation-based education
    (2019) Swart, Robert Nicholas; Duys, Rowan
    Background: Simulation-based education (SBE) has been shown to be an effective and reproducible learning tool. SBE is used widely internationally. The current state of SBE in South Africa is unknown. To the best of our knowledge this is the first survey that describes the use and attitudes towards SBE within South Africa. Methods: An online survey tool was distributed by email to: i) the South African Society of Anaesthesiologists (SASA) members; and ii) known simulation education providers in South Africa. The respondents were grouped into anaesthesia and non-anaesthesia participants. Descriptive statistics were used to analyse the data. Ethics approval was obtained: HREC REF 157/2017. Results: The majority of the respondents provide SBE and integrate it into formal teaching programmes. There is a will amongst respondents to grow SBE in South Africa, with it being recognised as a valuable educational tool. The user groups mainly targeted by SBE, were undergraduate students, medical interns, registrars and nurses. Learning objectives targeted include practical skills, medical knowledge, critical thinking and integrated management. Amongst anaesthesia respondents: the tool most commonly used to assess the quality of learner performance during SBE, for summative assessment, was ‘expert opinion’ (33%); the most frequent methods of evaluating SBE quality were participant feedback (42%) and peer evaluation (22%); the impact of SBE was most frequently assessed by informal discussion (42%) and learner feedback (39%). In anaesthesia SBE largely takes place within dedicated simulation facilities on site (47%). Most respondents report access to a range of SBE equipment. The main reported barriers to SBE were: finance, lack of trained educators, lack of equipment and lack of protected time. A limited number of respondents report engaging in SBE research. There is a willingness in both anaesthesia and non-anaesthesia groups (96% and 89% respectively) to collaborate with other centres. Conclusion: To the best of our knowledge this publication provides us with the first cross sectional survey of SBE in anaesthesia and a selection of non-anaesthetic respondents within South Africa. The majority of respondents indicate that SBE is a valuable education tool. A number of barriers have been identified that limit the growth of SBE within South Africa. It is hoped that with a commitment to ongoing SBE research and evaluation, SBE can be grown in South Africa.
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    Statistical model selection techniques for the cox proportional hazards model: a comparative study
    (2022) Njati, Jolando; Gumedze, Freedom
    The advancement in data acquiring technology continues to see survival data sets with many covariates. This has posed a new challenge for researchers in identifying important covariates for inference and prediction for a time-to-event response variable. In this dissertation, common Cox proportional hazards model selection techniques and a random survival forest technique were compared using five performance criteria measures. These performance measures were concordance index, integrated area under the curve, and , and R2 . To carry out this exercise, a multicentre clinical trial data set was used. A simulation study was also implemented for this comparison. To develop a Cox proportional model, a training dataset of 75% of the observations was used and the model selection techniques were implemented to select covariates. Full Cox PH models containing all covariates were also incorporated for analysis for both the clinical trial data set and simulations. The clinical trial data set showed that the full model and forward selection technique performed better with the performance metrics employed, though they do not reduce the complexity of the model as much as the Lasso technique does. The simulation studies also showed that the full model performed better than the other techniques, with the Lasso technique overpenalising the model from the simulation with the smaller data set and many covariates. AIC and BIC were less effective in computation than the rest of the variable selection techniques, but effectively reduced model complexity than their counterparts for the simulations. The integrated area under the curve was the performance metric of choice for choosing the final model for analysis on the real data set. This performance metric gave more efficient outcomes unlike the other metrics on all selection techniques. This dissertation hence showed that variable selection techniques differ according to the study design of the research as well as the performance measure used. Hence, to have a good model, it is important to not use a model selection technique in isolation. There is therefore need for further research and publish techniques that work generally well for different study designs to make the process shorter for most researchers.
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    THE CENTRAL SLOPE OF DARK MATTER CORES IN DWARF GALAXIES: SIMULATIONS VERSUS THINGS
    (2011) Oh, Se-Heon; Brook, Chris; Governato, Fabio; Brinks, Elias; Mayer, Lucio; de Blok, W J G; Brooks, Alyson; Walter, Fabian
    We make a direct comparison of the derived dark matter (DM) distributions between hydrodynamical simulations of dwarf galaxies assuming ACDM cosmology and the observed dwarf galaxies sample from the THINGS survey in terms of (1) the rotation curve shape and (2) the logarithmic inner density slope a of mass density profiles. The simulations, which include the effect of baryonic feedback processes, such as gas cooling, star formation, cosmic UV background heating, and most importantly, physically motivated gas outflows driven by supernovae, form bulgeless galaxies with DM cores. We show that the stellar and baryonic mass is similar to that inferred from photometric and kinematic methods for galaxies of similar circular velocity. Analyzing the simulations in exactly the same way as the observational sample allows us to address directly the so-called cusp/core problem in the ACDM model. We show that the rotation curves of the simulated dwarf galaxies rise less steeply than cold dark matter rotation curves and are consistent with those of the THINGS dwarf galaxies. The mean value of the logarithmic inner density slopes alpha of the simulated galaxies' DM density profiles is similar to-0.4 +/- 0.1, which shows good agreement with alpha = -0.29 +/- 0.07 of the THINGS dwarf galaxies. The effect of non-circular motions is not significant enough to affect the results. This confirms that the baryonic feedback processes included in the simulations are efficiently able to make the initial cusps with alpha similar to-1.0 to -1.5 predicted by DM-only simulations shallower and induce DM halos with a central mass distribution similar to that observed in nearby dwarf galaxies.
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    Tobacco Excise Simulation Model (TETSiM)
    (2010) Van Walbeek, Corne
    Tool for tobacco control advocates and government officials considering the impact of a change in tobacco excise taxes on a number of variables. Useful simulation for considering impact of changes in tobacco excise taxes on a number of variables. By changing some of the input parameters, you can see how this affects the output values.
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    Vector theories in cosmology
    (2010) Esposito-Farèse, Gilles; Pitrou, Cyril; Uzan, Jean-Philippe
    This article provides a general study of the Hamiltonian stability and the hyperbolicity of vector field models involving both a general function of the Faraday tensor and its dual, $f(F2,Ftilde F)$, as well as a Proca potential for the vector field, $V(A2)$. In particular it is demonstrated that theories involving only $f(F2)$ do not satisfy the hyperbolicity conditions. It is then shown that in this class of models, the cosmological dynamics always dilutes the vector field. In the case of a nonminimal coupling to gravity, it is established that theories involving $R f(A2)$ or $Rf(F2)$ are generically pathologic. To finish, we exhibit a model where the vector field is not diluted during the cosmological evolution, because of a nonminimal vector field-curvature coupling which maintains second-order field equations. The relevance of such models for cosmology is discussed. Comment: 17 pages, no figure