A research report Submitted to the School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Masters of Science in Epidemiology and Biostatistics 15 June 2017, Johannesburg, South Africa / Introduction: Worldwide, cardiovascular diseases are the number one cause of death with a three-quarter of cardiovascular disease deaths occurring in low-middle income countries. Childhood social adversity as a proxy of psychosocial stress has been found to be associated with later adult risk of cardiovascular diseases, with studies investigating the mechanisms linking early exposure to social adversity and later risk of cardiovascular diseases. CRP has been a biomarker that is found to be associated with the risk of cardiovascular diseases in adults, however, the association between CRP levels in adolescence and social adversity in children (prenatal and postnatal periods) is not well documented. Assessing the association between childhood social adversity and CRP levels in late adolescent period will encourage further studies to explore whether high levels of CRP tracks from adolescence to adulthood and ultimately increase the risk of cardiovascular diseases in the South African context. Aim: This study aims to determine the association between social adversity from the prenatal period to two years of age and the level of CRP in the same cohort at the age of 18 (from 1990 to 2008) Methods: The study was a secondary data analysis of the Birth to Twenty longitudinal study which recruited 3273 singleton children. Four measures (prenatal and postnatal (0-2 years)) of social adversity in children (which are maternal prenatal stress, maternal prenatal general feeling, maternal postnatal depression and household socioeconomic status) were used. The high-sensitivity C-reactive protein was grouped into tertiles (1st tertile: hs-CRP<0.48 mg/l, 2nd tertile: 0.48<hs-CRP<1.16, 3rd tertile: hs-CRP>1.16) and multinomial logistic regressions were therefore used to assess the association between childhood social adversities and tertiles of high sensitivity C-reactive protein. Results: The primary Birth to Twenty longitudinal study had more than 35% loss to follow-up at 18 years. No statistically significant difference (p>0.05) was found on demographic variables of those included in the analysis compared to those not included (due to current study criteria and loss to follow-up). A unit increase in maternal marital stress score during pregnancy was associated with an increase by 2.23 (p=0.03) in the relative risk of the youth being in the 2nd high sensitivity C-reactive protein tertile in comparison to being in the 1st high sensitivity C-reactive protein tertile. For a unit increase in maternal family stress score, the relative risk of the youth being in the 3rd high sensitivity C-reactive protein is 1.61 (p=0.04) times greater in comparison to being in the 1st high sensitivity C-reactive protein tertile. No statistically significant associations were observed among the other categories of social adversity (p>0.05) and high sensitivity C-reactive proteins. Low social support to mothers during pregnancy was associated with elevated high-sensitivity C-reactive protein in adolescents. Conclusion: A positive association was observed between a prenatal measure of social adversity and elevated high-sensitivity C-reactive protein; In particular, increased levels of family and relationship-related prenatal stress during pregnancy is a predictor of elevated high-sensitivity C-reactive protein in children. This study contributes to the empirical evidence from studies done in animals suggesting that early development of adult health complication starts during the intrauterine period. The findings of this study will further guide intervention research to target conditions during intrauterine period in preventing adult health complications. / MT2017

No description available.

No description available.

none

The MixAlco process, a proprietary technology owned by Texas A&M University, converts biomass (e.g., municipal solid waste, sewage sludge, paper, agricultural residues, and energy crops) into usable chemicals (e.g., acetic acid) and fuels (e.g., ethanol). Historically, calcium carbonate has been used as the buffer. Recently, it was found that using ammonium bicarbonate as the buffering agent enhances the fermentation conversion. In this case, fermentation broth contains ammonium salts (e.g., ammonium acetate, propionate, butyrate, pentanoate). Therefore, the downstream processing steps (including extraction, purification, esterification, and product separation) must be compatible with the ammonium carboxylate salts formed in the fermentation. This research focuses on converting fermentation broth carboxylate salts into their corresponding acids via "acid springing." Reactive extraction and thermal conversion (distillation) are crucial parts of the acid springing process. Because the components of the fermentation broth are over 80% ammonium acetate and 20% other ammonium carboxylate salts (ammonium propionate, butyrate, pentanoate, etc.), all the initial experiments in this study were performed using reagentgrade ammonium acetate to simplify the reaction. Later, actual fermentation broth was employed. The primary objective of this study was to provide the optimal operating conditions to make the downstream processing steps of the MixAlco process compatible with ammonium carboxylate salts formed in the fermentation. The optimal initial concentration for reactive extraction should be 150-200 g/L and the volume ratio of aqueous phase and extractant should be 1:1. The distribution coefficient reaches the maximum value when the concentration of TOA is 20% (vol %) in n-octanol. The batch distillation study shows that there are two reaction stages: (1) water leaves the system at 100-106 °C and (2) the acid-amine complex decomposes at 160-180 °C.

Reactive distillation is a combination of a traditional multi-stage distillation column with a chemical reaction. The primary benefits of a reactive distillation process are reduced capital costs for equipment and energy in addition to enhanced conversion for equilibrium-limited reactions. One such equilibrium-limited reaction is an olefin metathesis. Olefin metathesis is a catalyzed reaction that breaks the double bond in olefins and rearranges the alkene fragments into new olefinic products. A comprehensive investigation of a reactive distillation based olefin metathesis and supporting experimentation is documented here. A small pilot plant study was performed for pilot scale performance comparison. Bench reactor experimentation was conducted for the purposes of learning detailed information on specific metathesis reactions. Lastly, a process simulation study was completed for comparison in performance with the small pilot plant process. The small pilot plant study involved the design, construction, testing, operation, and optimization of a reactive distillation column. Continuous operation campaigns at two different hydraulic capacities within the reactive zone were performed and their performances were compared. A higher hydraulic capacity proved to be more efficient and more selective for the conversion of medium molecular weight olefins into both lighter and heavier olefinic products. Bench reactor experiments were designed with the intent of investigating specific alpha olefin metathesis reactions and obtaining conversions, selectivities, and yield structures for future simulation work. However, under conditions similar to that within the small pilot plant process, there existed a high frequency of secondary double bond isomerization (possibly due to an isomerization activity for alumina). There was also an observed dependence on temperature for both the primary metathesis and secondary isomerization reactions. A process simulation representative of the small pilot plant process was constructed in AspenPlus. Using a simplified reaction network based on assumptions and analysis of the reactive zone, its performance was compared with that of the small pilot plant process. The simulation performance tended to underpredict overhead compositions, but accurately simulated the bottoms product composition. Because reactive distillation has not been used with a heavy olefin metathesis reaction, this dissertation demonstrates the uniqueness and effectiveness of a reactive distillation based heavy olefin metathesis. / text

In the mantle section of many ophiolite sequences, dunite dikes are present. Around dunite dikes at the Josephine and Trinity ophiolite, a sequence of lithologies consisting of plagioclase lherzolite, lherzolite, and harzburgite is present. This sequence of rocks has been interpreted to be the result of reactive porous flow. From trace element data, the mafic melt has been interpreted to flow both into and out of the dunite dikes. Whether the melt emanates from the dunite bodies or is collected by them has implications for the mechanisms of melt extraction beneath ridge systems. The determination of the flow direction based on tracer distributions is difficult and therefore additional constraints are important. Reactive transport theory predicts that lithological zonations around dunite bodies can indicate the direction of flow. To date no reactive transport model has been developed to test these hypotheses, and therefore I have built a reactive transport model using COMSOL v. 4.1. I developed a model for an orthopyroxene dissolution front based on the model of Chadam et al. (1986, Reactive infiltration instabilities, IMA Journal of Applied Mathematics, v. 36, p.207-221). This model includes the strong nonlinearity feedback that has been invoked to lead to the channelization of melt flow. The instability leads to the formation of elongated regions where orthopyroxene is depleted. This model predicts that the melt is focused into the dunite bodies, most flow is parallel to the dunite boundaries, and exits the fingers at the tip of the column. / text

No description available.

This thesis attempts to investigate the performance of various reactive power compensation devices, examine the mechanism of reactive power compensation for HVDC systems, and develop guidelines for the design of reactive power compensation schemes for HVDC systems. The capabilities of various reactive power compensators to enhance power system stability are compared in both steady and transient states. An understanding of the capabilities of these compensators provides a basis for further investigation of their performance in HVDC systems. The reactive power requirements of HVDC converters are studied. The voltage dependencies of the HVDC converters at different control modes are derived, which allow for predictions of how HVDC converters impact AC system voltage stability. The transient performance of reactive power compensation options for HVDC Systems is studied by comparing their behavior during DC fault recovery, Temporary Overvoltage (TOV), and commutation failure. How to quantify the system strength when reactive compensators are connected to the converter bus is investigated. A new series of indices are developed based on the Apparent Short Circuit Ratio Increase (ASCRI). The inertia of a synchronous condenser and its impact on the frequency stability of an AC/DC system are discussed. By modelling the inverter side AC system in greater detail, the frequency stability and rotor angle stability following fault transients is examined based on time domain simulation. Finally, a guideline for designing dynamic reactive power compensation for HVDC systems is proposed.

No description available.