Global ETD Search

1	Modelling of highly skewed longitudinal count data based on the discrete Weibull distribution Nel, Helene Mari January 2021 (has links) Longitudinal data refer to multiple observations collected on the same subject (or unit) over time. Zero-inflated data (containing many zeros) frequently occur, resulting in overdispersion in count data. Regression models used to analyze count data are often based on the Poisson and negative binomial (NB) distribution. The Poisson distribution is restrictive when count data are overdispersed; the regression model can, therefore, give inappropriate fits when the variability in the data is larger or smaller than the theoretical variance. These two cases are, respectively, referred to as overdispersion and underdispersion. The NB distribution handles overdispersed data better compared to the Poisson distribution, but not underdispersed data. Another problem with the NB distribution is that it does not accommodate heavy-tailed or highly skewed data well. In this study, the discrete Weibull (DW) and the zero-inflated DW (ZIDW) distributions are explored in a mixed model context that models the median using a Bayesian approach. In contrast, the conventional NB and ZINB mixed-effects regression models model the mean counts over time. Results from the four mixed-effects regression models are compared. It is observed that the Bayesian DW and ZIDW mixed-effects regression models are computationally competitive with the Bayesian NB and ZINB mixed-effects regression models concerning flexibility, implementation, and convergence speed. The DW and ZIDW models are found to be excellent choices to model highly skewed longitudinal count data. / Mini Dissertation (MSc (Advanced Data Analytics))--University of Pretoria, 2021. / NRF / Statistics / MSc (Advanced Data Analytics) / Unrestricted UCTD Mathematical statistics 895 (WST 895)
2	Modelování odezvy zkušebních těles ze stavebních materiálů při lomových experimentech / Modelling the response of building material specimens during fracture tests Navrátil, Petr January 2012 (has links) The thesis focuses on the computational simulation of wedge splitting test of a concrete specimen by using finite element method. Different levels of numeric model for different notch depth and for different position of support are solved. Depending on the depth of a notch and difference of configuration, the crack paths and responses to an exterior load on a crack mouth opening displacement are evaluated.
3	Wirkung physiko-chemischer Oberflächencharakteristika auf Zytotoxizität verschiedener dentaler Komposite / Effect of physicochemical surfaces Characteristics of cytotoxicity of various dental composites Kurbad, Oliver 16 May 2019 (has links) No description available. 610 Komposit L929 GF1 Rauheit Oberflächenenergie WST 8 LDH-Cytotoxicity-Assay Zytotoxizität Viabilität adhärente Zellen dental composite L929 roughness surface energy WST 8 LDH-Cytotoxicity assay cytotoxicity viability adherent cells GF1 Medizin (PPN619874732)
4	Activin A und Follistatin bei bakteriellen Infektionen - Der Einfluss von Activin A auf Mikrogliazellen in vitro und der Einfluss von Follistatin auf den Verlauf einer E. coli-K1-Sepsis im Mausmodell / Activin A und Follistatin during bacterial infections - The effect of Activin A on microglial cells in vitro and the influence of Follistatin on the course of E. coli K1 sepsis in a mouse model Dießelberg, Catharina 19 June 2012 (has links) No description available. 610 Medizin, Gesundheit MED 000 MED 331 MED 334 MED 530 Medicine Activin A Follistatin Meningitis Sepsis Mikroglia Mausmodell E. coli Phagozytose NO TNF-α WST Seiltest Überleben Activin A Follistatin Meningitis Sepsis microglia mouse model E. coli phagocytosis NO TNF-α WST tightrope test survival 44 44. 43 44.75
5	Increasing the impact of ICT in language learning : investigating the effect of teachers' ownership of microblending CALL in the classroom within the WST model of ICT use Bish, David William January 2017 (has links) This thesis aims to address why the adoption of CALL (Computer Assisted Language Learning) within the language classroom is so varied, and its success so unclear, despite fifty years of investment and research. The huge promise of ICT (Information and Communications Technology) driven results has created an imbalance in language teaching, where initiatives are brought about from outside the classroom, with teachers held accountable for their adoption. My reading of the literature is that lack of consideration of the teacher’s role in implementation of classroom technology has led to mismatched expectations and performance. If the nature of the teacher’s contribution is recognized, I believe that this can lead to more effective use of ICT, which I have set out to show. My study, based on a survey of 319 EFL (English as a Foreign Language) teachers across the international group of 31 schools in which I work, seeks to put the teacher back into the picture by examining where their enacted beliefs in social constructivist pedagogy best align with classroom use of digital technology. I coin this emerging praxis ‘microblending’, a pedagogy rooted in Second Language Acquisition (SLA) theory and contemporary methodology, and I seek to demonstrate its relevance in this study I test the viability of measuring teacher’s microblending readiness through application of Technology Acceptance Modelling (TAM) in an EFL setting to produce a model that explains the variation in classroom use of ICT. My model is based on a critical replication of the WST (‘Will, Skill, Tool’) model, a TAM model which has so far only been used in mainstream classroom teaching. I have updated, created and piloted new instruments within the scope of the study, which are now already in use within the institution where I carried out my investigations. Using both linear regression and Structural Equation Modelling (SEM) techniques I explored how these measurements of the learning environment can explain a teacher’s application of technology. This first attempt appears to explain over 89% of the variation in classroom use of technology, which already exceeds the predictive power of several contemporary models in use in parallel fields of education. Given further work to refine and apply the model, a valuable improvement could be made in how teachers work with ICT in the language classroom for improved learning outcomes.
6	Synthesis, optical and morphological characterization of pbse quantum dots for diagnostic studies: a model study Ouma, Linda Achiengꞌ January 2013 (has links) >Magister Scientiae - MSc / In this study PbSe quantum dots (QDs) were successfully synthesized via the organometallic and aqueous routes. Optical characterization was carried out using photoluminescence (PL) spectroscopy, structural and morphological characterization were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Energy-dispersive X-ray spectroscopy (EDS) was used to determine the composition of the QDs. All the synthesized QDs were found to have emissions within the near-infrared region of the spectrum (≥1000 nm) with most of them being less than 5 nm in size. The aqueous synthesized QDs had a perfect Gaussian emission spectrum with a FWHM of ~23 nm indicating pure band gap emission and narrow size distribution respectively. The QDs were determined to have a cubic rock-salt crystal structure consistent with bulk PbSe. The aqueous synthesized QDs were however not stable in solution with the QDs precipitating after approximately 48 h. The organometallic synthesized QDs were transferred into the aqueous phase by exchanging the surface oleic acid ligands with 11-mercaptoundecanoic acid ligands. The ligand exchanged QDs were however stable in solution for over two weeks. The effects of reaction parameters on the optical and structural properties of the organometallic synthesized QDs were investigated by varying the reaction time, temperature, ligand purity, lead and selenium sources. It was observed that larger QDs were formed with longer reaction times, with reactions proceeding faster at higher reaction temperatures than at lower temperatures. Varying the ligand purity was found to have minimal effects on the properties of the synthesized QDs. The lead and selenium sources contributed largely to the properties of the QDs with lead oxide producing spherical QDs which were smaller compared to the cubic QDs produced from lead acetate. TBPSe was seen to produce smaller QDs as compared to TOPSe. The cytotoxity of the synthesized QDs was determined following the WST-1 cell viability assay with the QDs being found to be non-toxic at all the tested concentrations PbSe Quantum dots (QDs) Semiconductor nanocrystals (NCs) Near-infrared (NIR) Organometallic synthesis Aqueous synthesis Ligand exchange Photoluminescence spectroscopy (PL) 3-Mercaptopropionic acid (MPA) 11-Mercaptoundecanoic acid (MUA) Water-soluble tetrazolium salt (WST-1)
7	Development of Sensitive In Vitro Assays to Assess the Ocular Toxicity Potential of Chemicals and Ophthalmic Products McCanna, David January 2009 (has links) The utilization of in vitro tests with a tiered testing strategy for detection of mild ocular irritants can reduce the use of animals for testing, provide mechanistic data on toxic effects, and reduce the uncertainty associated with dose selection for clinical trials. The first section of this thesis describes how in vitro methods can be used to improve the prediction of the toxicity of chemicals and ophthalmic products. The proper utilization of in vitro methods can accurately predict toxic threshold levels and reduce animal use in product development. Sections two, three and four describe the development of new sensitive in vitro methods for predicting ocular toxicity. Maintaining the barrier function of the cornea is critical for the prevention of the penetration of infections microorganisms and irritating chemicals into the eye. Chapter 2 describes the development of a method for assessing the effects of chemicals on tight junctions using a human corneal epithelial and canine kidney epithelial cell line. In Chapter 3 a method that uses a primary organ culture for assessing single instillation and multiple instillation toxic effects is described. The ScanTox system was shown to be an ideal system to monitor the toxic effects over time as multiple readings can be taken of treated bovine lenses using the nondestructive method of assessing for the lens optical quality. Confirmations of toxic effects were made with the utilization of the viability dye alamarBlue. Chapter 4 describes the development of sensitive in vitro assays for detecting ocular toxicity by measuring the effects of chemicals on the mitochondrial integrity of bovine cornea, bovine lens epithelium and corneal epithelial cells, using fluorescent dyes. The goal of this research was to develop an in vitro test battery that can be used to accurately predict the ocular toxicity of new chemicals and ophthalmic formulations. By comparing the toxicity seen in vivo animals and humans with the toxicity response in these new in vitro methods, it was demonstrated that these in vitro methods can be utilized in a tiered testing strategy in the development of new chemicals and ophthalmic formulations. in vitro Alternative Methods alamarBlue rhodamine tight junctions bovine lens viability toxicity mitochondria mitochondria integrity benzalkonium chloride sodium dodecyl sulphate sodium lauryl sulfate scanning electron microscopy Draize Draize maximal average scores zonula occludens cosmetic directive PETA humane society animal league ICCVAM ECVAM JaCVAM BCOP bovine cornea ocular irritants ocular irritation ocular toxicity human corneal epithelial cells vitro confocal confocal microscopy metabolic activity optical quality reactive oxygen species contact lens contact lens care solutions barrier function microbial keratitis mulitipurpose solutions tight junction cell damage claudin ZO-1 occludin MDCK Madin Madin-Darby canine kidney cells cornea human cornea human corneal epithelium epithelial cell line human corneal epithelial cell line sodium fluorescein sodium fluorescein permeability fluorescein permeability ocular surface cell monolayer Araki-Sasaki cell physiology risk assessment safety assessment ScanTox scanning laser lens epithelium corneal cells in vitro model ophthalmic formulations multiple instillation back vertex animal testing rabbit testing alternatives to animal testing cultured bovine lens toxicity of chemicals irritation irritants laser scanner organ culture delayed toxicity toxins hydrogen peroxide cornea toxicity cornea toxicity models prediction of human toxicity no observable adverse effect level lowest observable adverse effect level NOAEL LOAEL toxicity thresholds safety factors cornea uncertainty factors preservatives disinfectants ophthalmic products preclinical preclinical testing epithelial barrier drug penetration clinical confocal microscopy animal rights rabbit cornea human cornea human clinical effects toxic animal rights activist sensitive measures toxic effect toxicity threshold agar overlay agar diffusion agar overlay method agar diffusion method cytochrome cytochrome c apoptosis necrotic apoptotic necrosis caspase rhodamine 123 resazuran resorufin cell death cell viability metabolic dye microsomal microsomal enzymes cytotoxicity cytotoxic cytotoxic effect MTT XTT WST-1 plasma membrane mitochondrial mitochondrial morphology ocular toxicity potential ocular toxicity human corneal epithelial cell line confocal analysis corneal epithelium cell fluorescence alamarBlue assay rhodamine dye animal welfare toxic injury degraded mitochondria epithelial monolayer disinfectants membrane integrity eye toxicity eye viability dye toxicity in humans human toxicity effects on the mitochondria mitochondrial toxicity in vitro battery in vitro test battery ophthalmic eye drop direct contact product safety cytotoxicity potential molecular molecular biology refine reduce replace sensitivity and relevance sensitivity relevance rabbit ocular irritation test product development cytotoxicity models cytotoxicity alternative methods replacements for animal testing three r's beagle tiered testing tiered testing strategy replacements animal testing mechanistic toxicity cornea mitochondria dose response threshold Vision Science and Biology
8	Development of Sensitive In Vitro Assays to Assess the Ocular Toxicity Potential of Chemicals and Ophthalmic Products McCanna, David January 2009 (has links) The utilization of in vitro tests with a tiered testing strategy for detection of mild ocular irritants can reduce the use of animals for testing, provide mechanistic data on toxic effects, and reduce the uncertainty associated with dose selection for clinical trials. The first section of this thesis describes how in vitro methods can be used to improve the prediction of the toxicity of chemicals and ophthalmic products. The proper utilization of in vitro methods can accurately predict toxic threshold levels and reduce animal use in product development. Sections two, three and four describe the development of new sensitive in vitro methods for predicting ocular toxicity. Maintaining the barrier function of the cornea is critical for the prevention of the penetration of infections microorganisms and irritating chemicals into the eye. Chapter 2 describes the development of a method for assessing the effects of chemicals on tight junctions using a human corneal epithelial and canine kidney epithelial cell line. In Chapter 3 a method that uses a primary organ culture for assessing single instillation and multiple instillation toxic effects is described. The ScanTox system was shown to be an ideal system to monitor the toxic effects over time as multiple readings can be taken of treated bovine lenses using the nondestructive method of assessing for the lens optical quality. Confirmations of toxic effects were made with the utilization of the viability dye alamarBlue. Chapter 4 describes the development of sensitive in vitro assays for detecting ocular toxicity by measuring the effects of chemicals on the mitochondrial integrity of bovine cornea, bovine lens epithelium and corneal epithelial cells, using fluorescent dyes. The goal of this research was to develop an in vitro test battery that can be used to accurately predict the ocular toxicity of new chemicals and ophthalmic formulations. By comparing the toxicity seen in vivo animals and humans with the toxicity response in these new in vitro methods, it was demonstrated that these in vitro methods can be utilized in a tiered testing strategy in the development of new chemicals and ophthalmic formulations. in vitro Alternative Methods alamarBlue rhodamine tight junctions bovine lens viability toxicity mitochondria mitochondria integrity benzalkonium chloride sodium dodecyl sulphate sodium lauryl sulfate scanning electron microscopy Draize Draize maximal average scores zonula occludens cosmetic directive PETA humane society animal league ICCVAM ECVAM JaCVAM BCOP bovine cornea ocular irritants ocular irritation ocular toxicity human corneal epithelial cells vitro confocal confocal microscopy metabolic activity optical quality reactive oxygen species contact lens contact lens care solutions barrier function microbial keratitis mulitipurpose solutions tight junction cell damage claudin ZO-1 occludin MDCK Madin Madin-Darby canine kidney cells cornea human cornea human corneal epithelium epithelial cell line human corneal epithelial cell line sodium fluorescein sodium fluorescein permeability fluorescein permeability ocular surface cell monolayer Araki-Sasaki cell physiology risk assessment safety assessment ScanTox scanning laser lens epithelium corneal cells in vitro model ophthalmic formulations multiple instillation back vertex animal testing rabbit testing alternatives to animal testing cultured bovine lens toxicity of chemicals irritation irritants laser scanner organ culture delayed toxicity toxins hydrogen peroxide cornea toxicity cornea toxicity models prediction of human toxicity no observable adverse effect level lowest observable adverse effect level NOAEL LOAEL toxicity thresholds safety factors cornea uncertainty factors preservatives disinfectants ophthalmic products preclinical preclinical testing epithelial barrier drug penetration clinical confocal microscopy animal rights rabbit cornea human cornea human clinical effects toxic animal rights activist sensitive measures toxic effect toxicity threshold agar overlay agar diffusion agar overlay method agar diffusion method cytochrome cytochrome c apoptosis necrotic apoptotic necrosis caspase rhodamine 123 resazuran resorufin cell death cell viability metabolic dye microsomal microsomal enzymes cytotoxicity cytotoxic cytotoxic effect MTT XTT WST-1 plasma membrane mitochondrial mitochondrial morphology ocular toxicity potential ocular toxicity human corneal epithelial cell line confocal analysis corneal epithelium cell fluorescence alamarBlue assay rhodamine dye animal welfare toxic injury degraded mitochondria epithelial monolayer disinfectants membrane integrity eye toxicity eye viability dye toxicity in humans human toxicity effects on the mitochondria mitochondrial toxicity in vitro battery in vitro test battery ophthalmic eye drop direct contact product safety cytotoxicity potential molecular molecular biology refine reduce replace sensitivity and relevance sensitivity relevance rabbit ocular irritation test product development cytotoxicity models cytotoxicity alternative methods replacements for animal testing three r's beagle tiered testing tiered testing strategy replacements animal testing mechanistic toxicity cornea mitochondria dose response threshold Vision Science and Biology

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