Essays on product quality in commercial aviation

Doctor of PhilosophyEconomicsPhilip G. GayleThis dissertation consists of three essays on product quality in commercial aviation. Since the mid-1990s, major airlines that serve the U.S. domestic market have increasingly found it appealing to form alliances. Amidst the recent emergence of airline alliance formation, this dissertation has sought to answer questions on the product quality implications of policies regarding cooperation among airlines in the U.S. domestic air travel industry. A challenge that empirical work faces in studying the relationship between airline alliances and product quality is to find reasonable measure(s) of product quality. The first essay sheds light on whether the route network integration that comes with an airline alliance provides sufficient extra incentive to partner carriers to improve their flight routing quality. Evidence suggests that routing quality for Delta/Continental/Northwest's--our alliance of interest--products decreases in markets where pre-alliance competition among alliance partners exists, resulting in substantial negative welfare effects for passengers. In fact, routing quality for Delta/Continental/Northwest products decreased by 0.256% below the mean routing quality of the entire sample's products. More interestingly, the codeshare effects in specific markets where the alliance firms competed prior to the alliance, are also negatively associated with routing quality of the alliance firms' products, resulting in a fall in consumer utility of $0.5 per consumer. The second essay explores the potential relationship between on-time performance and airline code-sharing. Although flight delay has always received much attention, we are unaware of any empirical research that measures the on-time performance effects of airline alliances. We empirically investigate the on-time performance effects of the largest U.S. domestic alliance that began in June 2003--an alliance between Delta Air Lines, Northwest Airlines and Continental Airlines. We find evidence that code-sharing improves alliance partners' on-time performance and that the size of the alliance effect on on-time performance depends on pre-alliance competition in a market, with the effect being larger in markets where the partners competed in prior to the alliance. Using a structural econometric model, the third essay attempts to provide an alternative explanation to a long-standing question: why are airlines late? Airlines usually claim that air travel delays are out of their control, placing the blame on adverse weather or air traffic control as the most common reasons. Despite these claims, data on causes of flight delay reveal that the share of delay caused by weather and air traffic control has been on the decline while the share of delay caused by airlines has been on the rise. This suggests that on-time performance improvement is well within the reach of carriers. We investigate why airlines have little or no incentive to improve on-time performance. We also measure the cost of delay borne by consumers in terms of how much monetary value they are willing to pay to avoid delay. We find that consumers are willing to pay$0.78 for every minute of arrival delay which after extrapolation, amounts to consumer welfare effects of $1.76 billion. Our findings suggest that airlines have little to no incentive because their markups do not increase when they improve on-time performance. In fact, the marginal increase in price resulting from on-time performance improvement is offset by an increase in marginal cost causing a zero net effect on markup

Bacterial vaginosis and risk factors: A cross-sectional study among women at Soa District Hospital, Cameroon

Bacterial vaginosis is the most prevalent genital infection, characterized by malodorous vaginal discharge, and has arisen as a public health concern due to its link to sexually transmitted illnesses. The purpose of this cross-sectional study was to determine the prevalence rate of bacterial vaginosis due to Gardnerella species and the risk factors related to this infection in childbearing women at the Hospital of District of Soa.  A questionnaire was administered before each vaginal swab sample was obtained. Bacterial vaginosis was classified as a Nugent score of 7 to 10, and the presence of clue cells. The findings were as follows: 210 women were enrolled in this study. The average age was 29.42±5.15 years, with extremes ranging from 18 to 48years. The age group with the highest representation (38.67%) was 26-33 years. The prevalence of bacterial vaginosis was 42.85% (90/210), with Gardnerella species present at 90% (81/90) and Mobiluncus species present at 3.33%. The 18-25 age group was more susceptible to bacterial vaginosis due to Gardnerellas pecies (35.80%), although the student group was the most affected (32.09%), and the difference was not statistically significant. With a prevalence of 44.44%, the single group was statistically significantly more exposed to this vaginal infection than the other groups. University-level women had a higher prevalence rate of bacterial vaginosis due to Gardnerella species infection (54.32%), followed by secondary-level women (37.03%). Gardnerella speciesvaginosis was found in both pregnant and non-pregnant women (38.27% and 61.72%, respectively). To avoid future obstetric difficulties, this infection must be effectively managed therapeuticall

Role of Gluconeogenesis and the Tricarboxylic Acid Cycle in the Virulence of \u3cem\u3eSalmonella enterica\u3c/em\u3e Serovar Typhimurium in BALB/c Mice

In Salmonella enterica serovar Typhimurium, the Cra protein (catabolite repressor/activator) regulates utilization of gluconeogenic carbon sources by activating transcription of genes in the gluconeogenic pathway, the glyoxylate bypass, the tricarboxylic acid (TCA) cycle, and electron transport and repressing genes encoding glycolytic enzymes. A serovar Typhimurium SR-11 Δcra mutant was recently reported to be avirulent in BALB/c mice via the peroral route, suggesting that gluconeogenesis may be required for virulence. In the present study, specific SR-11 genes in the gluconeogenic pathway were deleted (fbp, glpX, ppsA, and pckA), and the mutants were tested for virulence in BALB/c mice. The data show that SR-11 does not require gluconeogenesis to retain full virulence and suggest that as yet unidentified sugars are utilized by SR-11 for growth during infection of BALB/c mice. The data also suggest that the TCA cycle operates as a full cycle, i.e., a sucCD mutant, which prevents the conversion of succinyl coenzyme A to succinate, and an ΔsdhCDA mutant, which blocks the conversion of succinate to fumarate, were both attenuated, whereas both an SR-11 ΔaspA mutant and an SR-11 ΔfrdABC mutant, deficient in the ability to run the reductive branch of the TCA cycle, were fully virulent. Moreover, although it appears that SR-11 replenishes TCA cycle intermediates from substrates present in mouse tissues, fatty acid degradation and the glyoxylate bypass are not required, since an SR-11 ΔfadD mutant and an SR-11 ΔaceA mutant were both fully virulent

Effet de la supplémentation du Pennisetum purpureum au concentré riche en protéines sur les performances de croissance des cobayes (Cavia porcellus L. 1758) femelles à l'Ouest Cameroun

The effect of supplementation of Pennisetum purpureum (Pp) to protein concentrate (PB) on the growth performance Cavia porcellus (L. 1758) was evaluated for 2 months at the application and Research of the University of Dschang (West-Cameroon). 16 guinea-pigs with a average weight of 281 ± 42.0 g were used randomly in four treatments T0 (Pp), T1 (Pp + 16 % PB), T2 (Pp + 17 % PB) and T3 (Pp + 18 % PB). Chemical analysis showed that the different food formulations are rich in protein (16 to 18%), crude fiber (10%), metabolizable energy (2827 to 2857 Kcal/KgMS), calcium (0.95 %) and phosphorus (0.58 %). Results of the growth parameters showed that mean weights of animals increased significantly (P <0.05) between treatments. Food consumption increased with the age of animals. Guinea-pigs of the control batch T0 (8704.5 ± 0.00 g) consumed more than those of other treatments. The average daily gain varied significantly (P <0.05) between treatments. The consumption index is high for animals of the T0 batch (96.2 ± 7.80) as against 66.8 ± 35.6; 52.3 ± 14.3; 60.4 ± 22.4 respectively for batches T1, T2 and T3. The treatment T1 was the best ration. Keywords: Cavia porcellus, growth, Pennisetum purpureum, proteins, West Cameroon.L’effet de la supplémentation du Pennisetum purpureum (P.p) au concentré riche en protéines brutes (PB) sur les performances de croissance Cavia porcellus (L. 1758) femelles a été évalué durant 2 mois à la ferme d’application et de recherche de l’Université de Dschang (Ouest-Cameroun). 16 cobayes de poids moyen 281± 42,0 g ont été utilisés et répartis de manière aléatoire en quatre traitements T0 (P.p), T1 (P.p + 16 % PB), T2 (P.p + 17 % PB) et T3 (P.p + 18 % PB). L’analyse chimique montre que les différentes formulations alimentaires sont riches en protéines (16 à 18 %), en cellulose brute (10 %), en énergie métabolisable (2827 à 2857 Kcal/Kg MS), en calcium (0,95 %) et en phosphore (0,58 %). Les résultats de paramètres de croissance ont montré que les poids moyens des animaux ont connu une augmentation significative (P < 0,05) entre les traitements. La consommation alimentaire a augmenté avec l’âge des animaux. Les cobayes du lot T0 (8704,5 ± 0,0 g) ont le plus consommé par rapport aux autres traitements. Le gain moyen quotidien a varié significativement (P<0,05) entre les traitements. L’indice de consommation est élevé chez T0 (96,2 ± 7,80) contre 66,8 ± 35,6; 52,3 ± 14,3 et 60,4 ± 22,4 respectivement pour T1, T2 et T3. Le traitement T1 est la meilleure ration. Mots clés: Cavia porcellus, croissance, Pennisetum purpureum, protéines, Ouest Cameroun. &nbsp

Viral suppression in adults, adolescents and children receiving antiretroviral therapy in Cameroon: Adolescents at high risk of virological failure in the era of "test and treat"

Background: After the launching of the "Test & Treat" strategy and the wider accessibility to viral load (VL), evaluating virological success (VS) would help in meeting the UNAIDS targets by 2020 in Cameroon.Setting and methods: Cross-sectional study conducted in the Chantal BIYA International Reference Centre for research on HIV/AIDS prevention and management (CIRCB), Yaounde, Cameroon; data generated between October 2016 and August 2017 amongst adults, adolescents and children at 12, 24, 36 and >= 48 months on ART. VS was defined as < 1000 copies/mL of blood plasma and controlled viremia as VL < 50 copies/mL. Data were analysed by SPSS; p < 0.05 considered as significant.Results: 1946 patients (70% female) were enrolled (1800 adults, 105 adolescents, 41 children); 1841 were on NNRTI-based and 105 on PI-based therapy; with 346 patients at M12, 270 at M24, 205 at M36 and 1125 at >= M48. The median (IQR) duration on was 48 months (24-48). Overall, VS was 79.4% (95% CI 77.6-81.2) and 67.1% (95% CI 64.9-69.1) had controlled viral replication. On NNRTI-based, VS was 79.9% vs. 71.4% on PIs-based, p = 0.003. By ART duration, VS was 84.1% (M12), 85.9% (M24), 75.1% (M36) and 77.2% (>= M48), p = 0.001. By age, VS was 75.6% (children), 53.3% (adolescents) and 81.1% (adults), p < 0.001.Conclusions: In this sub-population of patients receiving ART in Cameroon, about 80% might be experiencing VS, with declining performance at adolescence, with NNRTI-based regimens, and as from 36 months on ART. Thus, improving VS may require an adapted adherence support mechanism, especially for adolescents with long-term treatment in resource-limited settings

po 8397 viral suppression among cameroonian adults adolescents and children receiving antiretroviral therapy in the test treat era

BackgroundGlobal efforts in meeting the 90–90–90 targets reveal that 70% of infected people know their HIV status, 77% of these are receiving antiretroviral therapy (ART) and 82% of treated patients have viral suppression. Since launching the 'test and treat' strategy and wider access to drugs that bring down the viral load (VL), evaluating viral suppression would help to identify those requiring interventions and to make progress towards meeting the targets in Cameroon.MethodsA study was conducted from October 2015 to August 2017 amongst adults (≥20 years), adolescents (10–19) and children (0–9) at 12, 24, 36 and ≥48 months on ART, monitored at the Chantal BIYA International Reference Centre for research on HIV/AIDS prevention and management (CIRCB) in Yaoundé, Cameroon. VL was established using Abbott m2000RT-PCR. VS was defined as VL <1000 copies/ml; with p<0,05 considered significant.ResultsA total of 1979 patients (70% female) were enrolled (1825 adults, 112 adolescents, 42 children); 1865 were on first-line (NNRTI-based, duration: 48 [IQR 24–48] months) vs. 114 on second-line (PI/r-based, duration: 48 [IQR 36–48] months); with 19%(368) at Month2, 14%(274) at Month24, 10%(207) at Month36% and 54% (1130) at ≥Month48. Overall, viral suppression was 79.4%, and 64.3% had controlled viral replication (VL <40). On first-line, viral suppression was 79.7% (1487) vs. 72.2%(83) on second-line (p=0,076). By ART duration, viral suppression was 83.4%(Month12), 85.8%(Month24), 74.9%(Month36) and 77.3% (≥Month48); p=0,0011. By age-range, viral suppression was 76.2% in children, 54.5% in adolescents, and 80.9% in adults (p<0,0001). By age and ART-regimen, viral suppression on first vs. second line was: children 76.5% vs. 60%; adolescents 51.7% vs. 65.2%; and adults 81.2% vs. 74.7%.ConclusionAbout 80% of Cameroonian patients might be experiencing viral suppression, with a declining performance at adolescence and by 3 years of ART experience. Thus, meeting the viral suppression target by 2020 requires a closer VL monitoring strategy and an adapted adherence support mechanism for adolescents living with HIV in resource-limited settings sharing similar challenges

Nutritional and Metabolic Requirements for the Infection of HeLa Cells by Salmonella enterica Serovar Typhimurium

Salmonella is the causative agent of a spectrum of human and animal diseases ranging from gastroenteritis to typhoid fever. It is a food - and water - borne pathogen and infects via ingestion followed by invasion of intestinal epithelial cells and phagocytic cells. In this study we employed a mutational approach to define the nutrients and metabolic pathways required by Salmonella enterica serovar Typhimurium during infection of a human epithelial cell line (HeLa). We deleted the key glycolytic genes, pfkA and pfkB to show that S. Typhimurium utilizes glycolysis for replication within HeLa cells; however, glycolysis was not absolutely essential for intracellular replication. Using S. Typhimurium strains deleted for genes encoding components of the phosphotransferase system and glucose transport, we show that glucose is a major substrate required for the intracellular replication of S. Typhimurium in HeLa cells. We also deleted genes encoding enzymes involved in the utilization of gluconeogenic substrates and the glyoxylate shunt and show that neither of these pathways were required for intracellular replication of S. Typhimurium within HeLa cells

An Incomplete TCA Cycle Increases Survival of Salmonella Typhimurium during Infection of Resting and Activated Murine Macrophages

In comparison to the comprehensive analyses performed on virulence gene expression, regulation and action, the intracellular metabolism of Salmonella during infection is a relatively under-studied area. We investigated the role of the tricarboxylic acid (TCA) cycle in the intracellular replication of Salmonella Typhimurium in resting and activated macrophages, epithelial cells, and during infection of mice.We constructed deletion mutations of 5 TCA cycle genes in S. Typhimurium including gltA, mdh, sdhCDAB, sucAB, and sucCD. We found that the mutants exhibited increased net intracellular replication in resting and activated murine macrophages compared to the wild-type. In contrast, an epithelial cell infection model showed that the S. Typhimurium ΔsucCD and ΔgltA strains had reduced net intracellular replication compared to the wild-type. The glyoxylate shunt was not responsible for the net increased replication of the TCA cycle mutants within resting macrophages. We also confirmed that, in a murine infection model, the S. Typhimurium ΔsucAB and ΔsucCD strains are attenuated for virulence.Our results suggest that disruption of the TCA cycle increases the ability of S. Typhimurium to survive within resting and activated murine macrophages. In contrast, epithelial cells are non-phagocytic cells and unlike macrophages cannot mount an oxidative and nitrosative defence response against pathogens; our results show that in HeLa cells the S. Typhimurium TCA cycle mutant strains show reduced or no change in intracellular levels compared to the wild-type. The attenuation of the S. Typhimurium ΔsucAB and ΔsucCD mutants in mice, compared to their increased net intracellular replication in resting and activated macrophages suggest that Salmonella may encounter environments within the host where a complete TCA cycle is advantageous