Genetic variants of the promoter of the heme oxygenase-1 gene and their influence on cardiovascular disease (The Ludwigshafen Risk and Cardiovascular Health Study)

Background Heme oxygenase-1 is an inducible cytoprotective enzyme which handles oxidative stress by generating anti-oxidant bilirubin and vasodilating carbon monoxide. A (GT)n dinucleotide repeat and a -413A>T single nucleotide polymorphism have been reported in the promoter region of HMOX1 to both influence the occurrence of coronary artery disease and myocardial infarction. We sought to validate these observations in persons scheduled for coronary angiography. Methods We included 3219 subjects in the current analysis, 2526 with CAD including a subgroup of CAD and MI (n = 1339) and 693 controls. Coronary status was determined by coronary angiography. Risk factors and biochemical parameters (bilirubin, iron, LDL-C, HDL-C, and triglycerides) were determined by standard procedures. The dinucleotide repeat was analysed by PCR and subsequent sizing by capillary electrophoresis, the -413A>T polymorphism by PCR and RFLP. Results In the LURIC study the allele frequency for the -413A>T polymorphism is A = 0,589 and T = 0,411. The (GT)n repeats spread between 14 and 39 repeats with 22 (19.9%) and 29 (47.1%) as the two most common alleles. We found neither an association of the genotypes or allelic frequencies with any of the biochemical parameters nor with CAD or previous MI. Conclusion Although an association of these polymorphisms with the appearance of CAD and MI have been published before, our results strongly argue against a relevant role of the (GT)n repeat or the -413A>T SNP in the HMOX1 promoter in CAD or MI

Flight Cancellation Behavior and Aviation System Performance

Flight cancellations are costly events for both airlines and passengers, yet are poorly understood. This dissertation expands upon literature that has studied flight cancellations by incorporating more variables and using advanced model specifications. In addition, it is necessary to understand the drivers of flight cancellations to quantify the relationship between flight cancellations and flight delay forecasts, which has been poorly documented in the literature. This dissertation investigates the factors leading to flight cancellations and quantifies the effect of flight cancellations on flight delay forecasts.First, econometric choice models are applied to a large dataset of historical flight information to determine the preferences and behaviors of airlines with respect to flight cancellations. The binary logit estimation results show that flight characteristics, such as load factor, distance, and flight frequency, are significant for determining the likelihood of flight cancellations, even when accounting for adverse weather effects. Airline-specific logit models indicate large heterogeneity with respect to flight cancellation tendencies across the industry. Inter-flight heterogeneity is explored through the use of mixed logit and latent class models, but lack of significant heterogeneity and long computation times provide evidence that a basic binary model can be sufficient for capturing the flight cancellation behavior of airlines. Cancellation predictions are made at an airport-level, but the distribution of predicted cancellations does not match well with the actual distribution observed in the data. Second, deterministic queueing methods are used to quantify the effect flight cancellations have on queueing delay forecasts. The cancellation model estimates are used to predict flight cancellations for a sample of all flights for 160 airport-days. The reductions in delay due to cancellations are captured using Monte Carlo simulation and a first-order approximation. The simulation results show that delays are reduced by 22% when considering the effect of cancellations and the first-order approximation results are no more than 4% larger than those from the Monte Carlo simulation.Finally, a case study was performed based on the current operating environment at San Francisco International Airport, where capacity reductions are expected during the summer of 2014 due to runway construction. Moreover, airlines are proposing schedules with 5% more demand. The increased schedule combined with the capacity decrease leads to an large increase in the queueing delay forecasts. A cancellation model is used to predict the changes in delay that result from cancellations induced by the change in operating conditions. The results from the cancellation model indicate that departure cancellations will increase at an almost one-to-one ratio with the proposed demand increase, thus negating any benefit to airlines from a denser schedule. The feedback of cancellations on queueing delay is further explored with analytical models. As witnessed in the case study, queueing delay can reach a theroetical maximum where any additions to the flight schedule results in higher queueing delays and an associated increase in flight cancellations that compensate for the additional flight and return the demand, and queueing delay, to its original level

Landing on empty: estimating the benefits from reducing fuel uplift in US Civil Aviation

Airlines and Air Navigation Service Providers are united in their goal to reduce fuel consumption. While changes to flight operations and technology investments are the focus of a number of studies, our study is among the first to investigate an untapped source of aviation fuel consumption: excess contingency fuel loading. Given the downside risk of fuel exhaustion of diverting to an alternate airport, airline dispatchers may load excess fuel onto an aircraft. Such conservatism comes at a cost of consuming excess fuel, as fuel consumed is a function of, among other factors, aircraft weight. The aim of this paper is to quantify, on a per-flight basis, the fuel burned due to carrying fuel beyond what is needed for foreseeable contingencies, and thereby motivate research, federal guidance, and investments that allow airline dispatchers to reduce fuel uplift while maintaining near zero risks of fuel exhaustion. We merge large publicly available aviation and weather databases with a detailed dataset from a major US airline. Upon estimating factors that capture the quantity fuel consumed due to carrying a pound of weight for a range of aircraft types, we calculate the cost and greenhouse gas emissions from carrying unused fuel on arrival and additional contingency fuel above a conservative buffer for foreseeable contingencies. We establish that the major US carrier does indeed load fuel conservatively. We find that 4.48% of the fuel consumed by an average flight is due to carrying unused fuel and 1.04% of the fuel consumed by an average flight is due to carrying additional contingency fuel above a reasonable buffer. We find that simple changes in flight dispatching that maintain a statistically minimal risk of fuel exhaustion could result in yearly savings of 338 million lbs of CO2, the equivalent to the fuel consumed from 4760 flights on midsized commercial aircraft. Moreover, policy changes regarding maximum fuel loads or investments that reduce uncertainty or increase the ability to plan flights under uncertainty could yield far greater benefits

Landing on empty: estimating the benefits from reducing fuel uplift in US Civil Aviation

Airlines and Air Navigation Service Providers are united in their goal to reduce fuel consumption. While changes to flight operations and technology investments are the focus of a number of studies, our study is among the first to investigate an untapped source of aviation fuel consumption: excess contingency fuel loading. Given the downside risk of fuel exhaustion of diverting to an alternate airport, airline dispatchers may load excess fuel onto an aircraft. Such conservatism comes at a cost of consuming excess fuel, as fuel consumed is a function of, among other factors, aircraft weight. The aim of this paper is to quantify, on a per-flight basis, the fuel burned due to carrying fuel beyond what is needed for foreseeable contingencies, and thereby motivate research, federal guidance, and investments that allow airline dispatchers to reduce fuel uplift while maintaining near zero risks of fuel exhaustion. We merge large publicly available aviation and weather databases with a detailed dataset from a major US airline. Upon estimating factors that capture the quantity fuel consumed due to carrying a pound of weight for a range of aircraft types, we calculate the cost and greenhouse gas emissions from carrying unused fuel on arrival and additional contingency fuel above a conservative buffer for foreseeable contingencies. We establish that the major US carrier does indeed load fuel conservatively. We find that 4.48% of the fuel consumed by an average flight is due to carrying unused fuel and 1.04% of the fuel consumed by an average flight is due to carrying additional contingency fuel above a reasonable buffer. We find that simple changes in flight dispatching that maintain a statistically minimal risk of fuel exhaustion could result in yearly savings of 338 million lbs of CO2, the equivalent to the fuel consumed from 4760 flights on midsized commercial aircraft. Moreover, policy changes regarding maximum fuel loads or investments that reduce uncertainty or increase the ability to plan flights under uncertainty could yield far greater benefits