A handbook for the estimation of airside delays at major airports (quick approximation method)

The handbook contains a set of curves that allow estimation of the average number of total daily delay minutes at a major airport under a variety of conditions. Demand profiles at each airport are classified with respect to the number of daily peak periods, the percentage of daily flights during peak periods, and the number of peak period operations at the airport. When combined with the saturation capacity of the airport, these descriptors provide sufficient information to allow usage of the handbook. Examples illustrating the use of the handbook are provided, as well as a brief review and description of the technical approach and of the computer package developed for this purpose

Il Caso del «Poligono di Quirra» alla luce della giurisprudenza della Corte europea dei diritti umani sulla tutela della salute e dell’ambiente

Fin dalla metà degli anni ’50, nell’area della Sardegna sudorientale denominata «Salto di Quirra», è operativo un «Poligono Sperimentale di Addestramento Interforze» (PISQ). Dalla sua istituzione a oggi, nel Poligono sono stati sperimentati e collaudati armamenti di vario tipo, che avrebbero diffuso nell’ambiente sostanze (anche radioattive, come il torio) sospettate di aver favorito l’insorgere di patologie tumorali letali in numerose persone che vivevano nelle zone limitrofe. Al riguardo, i mezzi di informazione hanno parlato di una vera e propria «Sindrome di Quirra»

Sartre, phenomenology and the study of social existence

[Δε διατίθεται περίληψη / no abstract available][Δε διατίθεται περίληψη / no abstract available

Potential impacts of advanced technologies on the ATC capacity of high-density terminal areas

Advanced technologies for airborne systems (automatic flight control, flight displays, navigation) and for ground ATC systems (digital communications, improved surveillance and tracking, automated decision-making) create the possibility of advanced ATC operations and procedures which can bring increased capacity for runway systems. A systematic analysis is carried out to identify certain such advanced ATC operations, and then to evaluate the potential benefits occurring over time at typical US high-density airports (Denver and Boston). The study is divided into three parts: (1) A Critical Examination of Factors Which Determine Operational Capacity of Runway Systems at Major Airports, is an intensive review of current US separation criteria and terminal area ATC operations. It identifies 11 new methods to increase the capacity of landings and takeoffs for runway systems; (2) Development of Risk Based Separation Criteria is the development of a rational structure for establishing reduced ATC separation criteria which meet a consistent Target Level of Safety using advanced technology and operational procedures; and (3) Estimation of Capacity Benefits from Advanced Terminal Area Operations - Denver and Boston, provides an estimate of the overall annual improvement in runway capacity which might be expected at Denver and Boston from using some of the advanced ATC procedures developed in Part 1. Whereas Boston achieved a substantial 37% increase, Denver only achieved a 4.7% increase in its overall annual capacity

Organic acid production in Aspergillus niger and other filamentous fungi

The aim of the thesis was to increase the understanding of organic acid production in Aspergillus niger and other filamentous fungi, with the ultimate purpose to improve A. niger as biotechnological production host. In Chapter 1, the use of microbial cell-factories for the production of various compounds of interest, with a focus on organic acid production in A. niger, is introduced. To convert A. niger into a cell-factory for the production of fumarate, an organic acid that this fungus does not naturally accumulate extracellularly, we need to know the key components that lead to high extracellular fumarate accumulation. This can be achieved by studying a natural fumarate producer, in our case the filamentous fungus Rhizopus delemar. To increase both the understanding of R. delemar fumarate production, and identify a possible candidate fumarate exporter protein for heterologuous expression in A. niger, we studied differences in the transcriptional and proteomic responses of R. delemar under high and low fumarate producing conditions, described in Chapter 2. Based on our analyses, we propose that a substantial part of the fumarate accumulated in R. delemar during nitrogen starvation results from the urea cycle due to amino acid catabolism. Thus, although we failed to identify the correct fumarte exporter (discussed in Chapter 8), the results of these analyses lead to a broader understanding of the mechanism underlying fumarate accumulation in R. delemar. In order to make A. niger a suitable production host for other organic acids, we also delved deeper into the understanding of why A. niger has an innate ability to secrete various organic acids, especially citrate, described in Chapter 3. We show that an increase in citrate secretion under iron limited conditions is a physiological response consistent with a role of citrate as A. niger iron siderophore. We found that A. niger citrate secretion increases with decreasing amounts of iron added to the culture medium and, in contrast to previous findings, this response is independent of the nitrogen source. Differential transcriptomics analyses of the two A. niger mutants NW305 (gluconate non-producer) and NW186 (gluconate and oxalate non-producer) revealed up-regulation of the citrate biosynthesis gene citA under iron limited conditions compared to iron replete conditions. In addition, we show that A. niger can utilise Fe(III) citrate as iron source. Finally, we discuss our findings in the general context of the pH-dependency of A. niger organic acid production, offering an explanation, besides competition, for why A. niger organic acid production is a sequential process influenced by the external pH of the culture medium. In Chapter 4, we further unravel the various different mechanisms underlying extracellular A. niger citrate accumulation. We show that the phenotype of increased extracellular citrate accumulation can have fundamentally different underlying mechanisms, depending on how this response was triggered. We found that varying the amount and supplement of an arginine auxotrophic A. niger strain induces increased citrate productivity. Transcriptomics analysis shows down-regulation of citrate metabolising enzymes in the conditions in which more citrate is accumulated extracellularly. This contrasts with the transcriptional adaptations triggered by iron limited conditions, described in Chapter 3. By combining data obtained from both experimental setups described in Chapters 3 and 4, we compiled a list of likely citrate transporter candidates. Two promising citrate exporter candidates were tested in the yeast Saccharomyces cerevisiae, of which one was successfully identified as citrate exporter. Our findings provide the first steps in untangling the complex interplay of different mechanisms underlying A. niger citrate accumulation, and we pinpoint, for the first time, a promising A. niger citrate exporter candidate, offering a valuable tool for improvement of A. niger as biotechnological cell-factory for citrate production. For the identification of different A. niger substrate importers, we combined in silico and in vivo approaches, and established a reliable pipeline to identify and test candidate transport proteins. The in silico approach, in which likely glucose transporter candidates are inferred from good matches with a glucose transporter specific Hidden Markov model (HMMgluT), and the in vivo approach, in which a sub-cellular proteomics approach is applied to isolate plasmalemmal glucose transporters, is described in Chapter 5. In the presented research work, a hidden Markov model (HMM), that shows a good performance in the identification and segmentation of functionally validated glucose transporters, was constructed. The model (HMMgluT) was used to analyse the A. niger membrane-associated proteome response to high and low glucose concentrations at a low pH. By combining the abundance patterns of the proteins found in the A. niger plasmalemma proteome with their HMMgluT scores, two new putative high affinity glucose transporters, denoted MstG and MstH, were identified. MstG and MstH were functionally validated and biochemically characterised by heterologous expression in a S. cerevisiae glucose transport null mutant. They were shown to be a high affinity glucose transporter (Km = 0.6 ± 0.1 mM) and a very high affinity glucose transporter (Km = 0.06 ± 0.005 mM) respectively. The concepts developed in Chapter 5 were applied in Chapter 6 to identify further substrate importer proteins in both A. niger and another filamentous fungus, Trichoderma reesei. Again a hidden Markov model, this time for the identification of xylose transporters, was constructed and used to analyse the A. niger and T. reesei in silico proteomes, yielding a list of candidate xylose transporters. From this list, three A. niger (XltA, XltB and XltC) and three T. reesei (Str1, Str2 and Str3) transporters were selected, functionally validated and biochemically characterised through their expression in a S. cerevisiae hexose transport null mutant, engineered to be able to metabolise xylose, but unable to transport this sugar. All six transporters were able to support growth of the engineered yeast on xylose, but varied in affinities and efficiencies in the uptake of the pentose. Amino acid sequence analysis of the selected transporters showed the presence of specific residues and motifs associated to xylose transporters. Transcriptional analysis of A. niger and T. reesei showed that XltA and Str1 were specifically induced by xylose and dependent on the XlnR/Xyr1 regulators, implying a biological role for these transporters in xylose utilisation. Thus, our findings show that our approach using HMMs is a robust pipeline to identify different substrate importer candidates. In Chapter 7, comparative plasmalemma proteomic analysis was used to identify candidate L-rhamnose transporters in A. niger. Further analysis was focused on protein ID 1119135 (RhtA) (JGI A. niger ATCC 1015 genome database). RhtA was classified as a Family 7 Fucose:H+ Symporter (FHS) within the Major Facilitator Superfamily. Family 7 currently includes exclusively bacterial transporters able to use different sugars. Strong indications for its role in L-rhamnose transport were obtained by functional complementation of the Saccharomyces cerevisiae EBY.VW.4000 strain in growth studies with a range of potential substrates. Biochemical analysis using L-[3H(G)]-rhamnose confirmed that RhtA is a L-rhamnose transporter. The RhtA gene is located in tandem with a hypothetical alpha-L-rhamnosidase gene (rhaB). Transcriptional analysis of rhtA and rhaB confirmed that both genes have a coordinated expression, being strongly and specifically induced by L-rhamnose, and controlled by RhaR, a transcriptional regulator involved in the release and catabolism of the methyl-pentose. RhtA is the first eukaryotic L-rhamnose transporter identified and functionally validated to date. In Chapter 8, the findings presented in this thesis with regards to our attempts at improving A. niger as biotechnological production host are summarised, and further implications for metabolic engineering approaches based on the conclusions drawn are discussed.</p

Time dependent estimates of delays and delay costs at major airports

January 1975Includes bibliographical references (p. 35)Two queuing models appropriate for estimating time dependent delays and delay costs at major airports are reviewed. The models use the demand and capacity profiles at any given airport as well as the number of runways there to compute bounds on queuing statistics. The bounds are obtained through the iterative solution of systems of equations describing the two models. This computational procedure is highly efficient and inexpensive. The assumptions and limitations of the models are discussed. Common characteristics and properties of delay profiles at major airport are illustrated through a detailed example. Potential applications to the exploration of the effect of air traffic control innovations on congestion and to the estimation of marginal delay costs are also described

Locating Mobile Servers on a Network with Markovian Processes

The median problem has been generalized to the case in which facilities can be moved, at a cost, on the network in response to changes in the state of the network. Such changes are brought about by changes in travel times on the links of the network due to the occurrence of probabilistic events. For the case examined here, transitions among states of the network are assumed to be Markovian. The problem is examined for an objective which is a weighted function of demand travel times and of facility relocation costs. It is shown that when these latter costs are a concave function of travel time, an optimal set of facility locations exists solely on the nodes of the network. The location-relocation problem is formulated as an integer programming problem and its computational complexity is discussed. An example illustrates the basic concepts of this paper

Congestion Mitigation through Schedule Coordination at JFK: An Integrated Approach

Most flight delays are created by large temporary or long-term imbalances between demand and capacity at the busiest airports. Absent large increases in capacity, airport congestion can only be mitigated through improvements in the utilization of available capacity and the implementation of demand management measures. This paper presents an integrated approach that jointly optimizes the airport’s flight schedule at the strategic level and the utilization of airport capacity at the tactical level, subject to scheduling and capacity constraints. The capacity utilization part involves controlling the runway configuration and the balance of arrival and departure service rates to minimize congestion costs. The schedule optimization reschedules a selected set of flights to reduce the demand-capacity mismatches while minimizing interference with airline competitive scheduling. We develop an original iterative solution algorithm that integrates airport stochastic queue dynamics and a Dynamic Programming model of airport operating procedures into an Integer Programming model of flight rescheduling. The algorithm is shown to converge in reasonable computational times and is thus implementable in practice. Extensive computational results for JFK Airport suggest that very substantial delay reductions can be achieved through limited changes in airline schedules. It is also shown that the proposed integrated approach to airport congestion mitigation performs significantly better than the typical sequential approach where scheduling and operational decisions are made separately

Endogenous Control of Service Rates in Stochastic and Dynamic Queuing Models of Airport Congestion

Airport congestion mitigation requires reliable delay estimates. This paper presents an integrated model of airport congestion that combines a tactical model of capacity utilization into a strategic queuing model. The model quantifies the relationships between flight schedules, airport capacity and flight delays, while accounting for the way arrival and departure service rates can be controlled over the day to maximize operating efficiency. We show that the model estimates well the average and variability of the delays observed at New York’s airports. Results suggest that delays can be extremely sensitive to even small changes in flight schedules or airport capacity

Airport quotas and peak hour pricing : theory and practice

Work performed by the Flight Transportation Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts; and sponsored the Office of Aviation Policy, Federal Aviation Administration, Department of Transportation, Washington, D.CMay 1976Includes bibliographical referencesThis report examines the leading theoretical studies not only of airport peak-hour pricing but also of the congestion costs associated with airport delays and presents a consistent formulation of both. The report also considers purely administrative measures, such as quotas, and hybrid systems which combine administrative and economic control techniques. These are all compared to the real-world situation and problems of implementation discussed. The actual experiences of the Port Authority of New York and New Jersey at the three major New York area airports and the British Airports Authority at Heathrow are then presented. Both organizations administer hybrid quota/ peak-hour pricing systems in conjunction with their respective air traffic control authorities. Their experience is compared with the theoretical analyses.Prepared under NASA Ames Research Cente