Runway Scheduling Using Generalized Dynamic Programming

A generalized dynamic programming method for finding a set of pareto optimal solutions for a runway scheduling problem is introduced. The algorithm generates a set of runway flight sequences that are optimal for both runway throughput and delay. Realistic time-based operational constraints are considered, including miles-in-trail separation, runway crossings, and wake vortex separation. The authors also model divergent runway takeoff operations to allow for reduced wake vortex separation. A modeled Dallas/Fort Worth International airport and three baseline heuristics are used to illustrate preliminary benefits of using the generalized dynamic programming method. Simulated traffic levels ranged from 10 aircraft to 30 aircraft with each test case spanning 15 minutes. The optimal solution shows a 40-70 percent decrease in the expected delay per aircraft over the baseline schedulers. Computational results suggest that the algorithm is promising for real-time application with an average computation time of 4.5 seconds. For even faster computation times, two heuristics are developed. As compared to the optimal, the heuristics are within 5 % of the expected delay per aircraft and 1 % of the expected number of runway operations per hour and can be 1000x faster

Quantitative comparisons of select cultured and uncultured microbial populations in the rumen of cattle fed different diets

<p>Abstract</p> <p>Background</p> <p>The number and diversity of uncultured ruminal bacterial and archaeal species revealed by 16S rRNA gene (<it>rrs</it>) sequences greatly exceeds that of cultured bacteria and archaea. However, the significance of uncultured microbes remains undetermined. The objective of this study was to assess the numeric importance of select uncultured bacteria and cultured bacteria and the impact of diets and microenvironments within cow rumen in a comparative manner.</p> <p>Results</p> <p>Liquid and adherent fractions were obtained from the rumen of Jersey cattle fed hay alone and Holstein cattle fed hay plus grain. The populations of cultured and uncultured bacteria present in each fraction were quantified using specific real-time PCR assays. The population of total bacteria was similar between fractions or diets, while total archaea was numerically higher in the hay-fed Jersey cattle than in the hay-grain-fed Holstein cattle. The population of the genus <it>Prevotella</it> was about one log smaller than that of total bacteria. The populations of <it>Fibrobacter succinogenes</it>, <it>Ruminococcus flavefaciens</it>, the genus <it>Butyrivibrio</it>, and <it>R. albus</it> was at least one log smaller than that of genus <it>Prevotella</it>. Four of the six uncultured bacteria quantified were as abundant as <it>F. succinogenes</it>, <it>R. flavefaciens</it> and the genus <it>Butyrivibrio</it>. In addition, the populations of several uncultured bacteria were significantly higher in the adherent fractions than in the liquid fractions. These uncultured bacteria may be associated with fiber degradation.</p> <p>Conclusions</p> <p>Some uncultured bacteria are as abundant as those of major cultured bacteria in the rumen. Uncultured bacteria may have important contribution to ruminal fermentation. Population dynamic studies of uncultured bacteria in a comparative manner can help reveal their ecological features and importance to rumen functions.</p