Elicitation of Subjective Probability Distributions

To incorporate expert opinion into a Bayesian analysis, it must be quantified as a prior distribution through an elicitation process that asks the expert meaningful questions whose answers determine this distribution. The aim of this thesis is to fill some gaps in the available techniques for eliciting prior distributions for Generalized Linear Models (GLMs) and multinomial models. A general method for quantifying opinion about GLMs was developed in Garthwaite and Al-Awadhi (2006). They model the relationship between each continuous predictor and the dependant variable as a piecewise-linear function with a regression coefficient at each of its dividing points. However, coefficients were assumed a priori independent if associated with different predictors. We relax this simplifying assumption and propose three new methods for eliciting positive-definite variance-covariance matrices of a multivariate normal prior distribution. In addition, we extend the method of Garthwaite and Dickey (1988) for eliciting an inverse chi-squared conjugate prior for the error variance in normal linear models. We also propose a novel method for eliciting a lognormal prior distribution for the scale parameter of a gamma GLM. For multinomial models, novel methods are proposed that quantify expert opinion about a conjugate Dirichlet distribution and, additionally, about three more general and flexible prior distributions. First, an elicitation method is proposed for the generalized Dirichlet distribution that was introduced by Connor and Mosimann (1969). Second, a method is developed for eliciting the Gaussian copula as a multivariate distribution with marginal beta priors. Third, a further novel method is constructed that quantifies expert opinion about the most flexible alternate prior, the logistic normal distribution (Aitchison, 1986). This third method is extended to the case of multinomial models with explanatory covariates. All proposed methods in this thesis are designed to be used with interactive Prior Elicitation Graphical Software (PEGS) that is freely available at http://statistics.open.ac.uk/elicitation

Dyslipidemia is the hallmark of the metabolic syndrome in postmenopausal women: Dyslipidemia in postmenopausal women

The incidence of cardiovascular diseases (CVD) increases after menopause and may be due to changes in the plasma lipid-lipoprotein levels that occur following menopausal transition. Physiological estrogen withdrawal during menopause plays a major role in abnormal lipid metabolism such as elevated low-density lipoprotein concentration. The aim of this study was to determine the relationship between dyslipidemia and the causative factors of metabolic syndrome in postmenopausal women. In this cross-sectional study, 290 postmenopausal Sudanese women were included. Lipid profiles were measured by spectrophotometer, estrogen hormone determined by ELISA, insulin resistance determined by HOMA-2 calculator and lipid accumulation product was calculated by the following equation (waist circumference in cm X triglyceride concentration in mM). The results revealed that total cholesterol, triglycerides, low-density lipoprotein levels and very low-density lipoprotein levels were significantly higher in the postmenopausal women with metabolic syndrome (MS) in comparison to those without the MS. Elevated total cholesterol levels were seen in 51.7 %, elevated triglycerides were seen in 49.7% and elevated low-density lipoprotein levels were seen in 29.3% whereas reduced high density lipoprotein levels were seen in 16.89% of the postmenopausal women. Total cholesterol, triglycerides and very low-density lipoprotein values showed a significant positive correlation with insulin resistance and lipid accumulation and a significant negative correlation with the estrogen hormone level. In addition, high density lipoproteins showed a significant negative correlation with lipid accumulation levels

An investigation of a heterogeneous aminohydroxylation catalyst.

Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.Os-Zn-Al hydrotalcite-like compounds (HTlc’s) were synthesised by the co-precipitation method and characterised using different techniques (powder XRD, ICP-OES, FT-IR spectroscopy, BET-surface area measurements, SEM and SEM-EDS, cryo-TEM, 27Al SS-NMR and TGA-DSC). The hydrotalcite-like catalyst was used to heterogenise the aminohydroxylation reaction. Among the three solvents investigated (toluene, MeCN/water (1:1 v/v) and t- BuOH/water (1:1 v/v)) in the aminohydroxylation reaction, toluene showed the slowest reaction rate, MeCN/water (1:1 v/v) and t-BuOH/water (1:1 v/v) demonstrated fast reaction rates comparable to each other. The reaction temperature was only significant when toluene was used as the solvent system (reaction time (100% depletion of starting material) and temperature are inversley proportional). The catalyst HTlc structure demonstrated a significant effect in terms of the reaction time and isolated yield of the -amino alcohols. Under the same testing conditions a heat treated catalyst (non-HTlc) showed a shorter reaction time, a reduction in the isolated yield of -amino alcohols with a rise in diol formation. All the different classes of olefins (aliphatic, aromatic, and functionalised) that were tested, gave 99.99% depletion of starting material. However, due to the same purification difficulties encountered in the homogeneous amino hydroxylation (AA) reaction, the isolated yield of -amino alcohols achieved here, ranged from 13 to 35 %, with the highest yield (35%) obtained when methylcinnamate was used as the olefin. Characterisation of the spent catalyst showed that HTlc structure is maintained, but crystallinity was lost (the material becomes polycrystalline) after the reaction. The leaching test showed that 4.5% and 5.5% of Os leached from the catalyst to the reaction solution when MeCN/water (1:1 v/v) and t-BuOH /water (1:1 v/v) were used as the solvent system, respectively. The leached form of Os was determined to be inactive, indicating that this system is truly heterogeneous. The recycling study (three cycles) indicated that the catalyst can be recycled, but with a decrease in the reaction rate (which could be due to structure defects and loss of crystallinity), and with no significant difference in the isolated yield of the amino-alcohol. The crystal structure of three -amino alcohols are also reported. The crystal structure of the - amino alcohol of cyclohexene, methylcinnamte and t-butylcrotonate were needle-like triclinic, pi, needle-like monoclinic, p21/c and cubic-like triclinic, p-1, respectively

Oxidative dehydrogenation of n-octane over molybdate based catalysts.

Ph. D. University of KwaZulu-Natal, Durban 2014.The oxidative dehydrogenation of n-octane over different molybdates was investigated using a continuous flow fixed bed reactor in the temperature range of 350-550 °C at 50 °C intervals. Molybdates investigated in this study were synthesized by the co-precipitation method and characterized by powder and in situ (oxidation and reduction) X-Ray diffraction (XRD), BETsurface area measurements, inductively coupled plasma-optical emission spectroscopy (ICPOES), Raman spectroscopy, scanning electron microscopy (SEM), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO). Molybdates focus of this study was magnesium molybdate (MM) and cobalt molybdate (CM). In the case of magnesium molybdate, catalysts with different magnesium : molybdenum ratios were synthesized (i.e. 0.87, 0.98, 1.06 and 1.25 magnesium : molybdenum). While for cobalt molybdate the ratio of cation to molybdenum was kept near the stoichiometric ratio. The influence of the synergistic effect between molybdenum trioxide and molybdate was investigated using MM. An increase of the molybdenum content in the catalysts resulted in an increase in the surface area of the catalysts and in the TPR results the intensity of the reduction peak corresponding to molybdenum trioxide increased as the molybdenum content increased, which marked an increase in the n-octane conversion. The preliminary catalytic testing was at a gas hourly space velocity (GHSV) of 4000 h-1 and carbon to oxygen ratio of 8:3 C:O. The highest conversion of n-octane and selectivity to value added products (i.e. octenes and aromatics) was obtained over the two catalysts with near stoichiometric ratio of molybdenum / magnesium (i.e. MM 0.98 and 1.06). The surface acidity of the catalysts was altered by varying the molybdenum content, which in return influenced the selectivity of the catalyst. Used catalyst characterization by Raman spectroscopy showed all catalysts were still dominated by the magnesium molybdate phase after the reaction. Both molybdates (i.e. MM and CM) with a near stoichiometric ratio of cation : molybdenum were tested under different oxidation environments ranging from oxygen lean to oxygen rich environments (i.e. carbon : oxygen ratio of 8:0, 8:1, 8:2, 8:3 and 8:4). The conversion of noctane over all molybdates increased as the oxygen concentration in the reaction feed increased. The carbon to oxygen ratio also greatly influences the selectivity of the catalyst. In general terms as the oxygen concentration increased the selectivity to octenes decreased and selectivity to aromatics increased, while the selectivity to COx increased and peaked at the reaction temperature close to the onset reduction temperature of the catalyst. The chemical stability of the catalyst was also altered by the oxygen concentration as determined by characterization of the used catalyst by powder XRD and Raman spectroscopy. In the case of MM and CM the initial phases of the catalyst was maintained and stable under moderate to oxygen rich environments (i.e. 8:2, 8:3 and 8:4 carbon : oxygen), while under oxygen lean environments (i.e. 8:0 and 8:1 carbon : oxygen) phase segregation takes place and molybdenum oxide dominates the catalysts. The effect of the cation in the molybdate structure was highlighted by comparing the activity and selectivity of the magnesium molybdate catalyst and the cobalt molybdate catalyst under isoconversion and iso-thermal conditions. Magnesium molybdate seems to favor olefin formation, while cobalt molybdate favors aromatics, based on the iso-conversion results. Considering the iso-thermal comparison between the two molybdates, the data indicate that cobalt molybdate is more active than magnesium molybdate

Optimization of a CMOS-MEMS Resonator for Applications of Relative Humidity Measurement

The mathematical modeling and the finite element analysis (FEA) of a Complementary Metal Oxide Semiconductor-Microelectromechanical System (CMOS-MEMS) resonator has been presented. The resonator is designed based on 0.35 µm CMOS foundry fabrication technology. The sensing principle of the resonator is based on the change in resonance frequency of the CMOS-MEMS resonator due to adsorption/absorption or desorption of humidity on the active material layer of deposited on the moving plate that results in changes in the mass of the device. Simple analytical models of the CMOSMEMS resonator are generated to achieve estimates of the device performs. The effect of changes in lengths and widths of the beams on spring constant, resonance frequency, damping coefficient and quality factor (Q) are investigated. The spring constant is found to decrease with increase the lengths of the beam and increasing with increase the widths of the beam

Effect of Microbial Inoculant on Fermentation Period and Chemical Composition of Sweet Sorghum Silage

Sorghum is one of the most suitable plants for silage production and becoming an increasingly important forage crop in many regions of the world. Due to its high water-soluble carbohydrates contents (WSC) and low buffer capacity, it is easy to ensile. This study evaluates the effect of adding Lactobacillus plantarum AZZ4 and Pediococcus acidilactici AZZ5 isolated from elephant grass on the fermentation period and chemical composition of sweet sorghum silage. Two strains of Lactobacillus plantarum subsp. Plantarum (AZZ4) , Pediococcus acidilactici (AZZ5), and one commercial bacteria Lactobacillus Plantarum, Ecosyl MTD/1(CB)) were chosen as additives at 6 log colony forming units (cfu)/g of fresh sweet sorghum grass in laboratory silos (1000g). Silos for each treatment were opened after 15,30, and 60d, respectively. Compared to the control, all the isolates improved the silage quality of sweet sorghum silage, indicated by significantly (P \u3c 0.05) lower ammonia nitrogen (NH3-N) content and undesirable microorganism counts, and higher lactic acid (LA) contents and ratios of lactic acid/acetic acid (LA/AA). During ensiling, AZZ4 performed better among all inoculants, indicated by a significantly (P \u3c 0.05) decrease in pH and ammonia- N contents and a higher increase in lactic acid contents

tert-Butyl 2-hy­droxy-3-(4-methyl­benzene­sulfonamido)­butano­ate

In the crystal of the title compound, C15H23NO5S, mol­ecules are linked through N—H⋯O and O—H⋯O hydrogen-bond inter­actions, resulting in centrosymmetric dimers in which the N—H⋯O inter­actions generate R 2 2(12) rings and the O—H⋯O inter­actions generate R 2 2(14) rings. Weak inter­molecular C—H⋯O inter­actions are also observed

Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

The preferential oxidation of CO (CO-PrOx) to CO2 is an effective catalytic process for purifying the H2 utilized in proton-exchange membrane fuel cells for power generation. Our current work reports on the synthesis, characterization and CO-PrOx performance evaluation of unsubstituted and magnesiumsubstituted iron- and cobalt-based oxide catalysts (i.e., Fe3O4 , Co3O4 , MgFe2O4 and MgCo2O4 ). More specifically, the ability of Mg to stabilize the MgFe2O4 and MgCo2O4 structures, as well as suppress CH4 formation during CO-PrOx was of great importance in this study. The cobalt-based oxide catalysts achieved higher CO2 yields than the iron-based oxide catalysts below 225 ◦C. The highest CO2 yield (100%) was achieved over Co3O4 between 150 and 175 ◦C, however, undesired CH4 formation was only observed over this catalyst due to the formation of bulk fcc and hcp Co0 between 200 and 250 ◦C. The presence of Mg in MgCo2O4 suppressed CH4 formation, with the catalyst only reducing to a CoO-type phase (possibly containing Mg). The iron-based oxide catalysts did not undergo bulk reduction and did not produce CH4 under reaction conditions. In conclusion, our study has demonstrated the beneficial effect of Mg in stabilizing the active iron- and cobalt-based oxide structures, and in suppressing CH4 formation during CO-PrO

(2R,3S)-Methyl 2-hy­droxy-3-(4-methyl­benzene­sulfonamido)-3-phenyl­propano­ate

In the title mol­ecule, C17H19NO5S, the p-tolyl ring is oriented approximately parallel to the phenyl ring [dihedral angle = 17.2 (1)°], resulting in an intra­molecular π–π inter­ation [centroid–centroid distance = 3.184 (10) Å]. In the crystal, mol­ecules are linked through O—H⋯O and C—H⋯O hydrogen bonds, forming hydrogen-bonded sheets lying diagonally across the ac face