Some measures of aircraft performance on the airport surface

May 1972Based upon a survey conducted at Boston and Atlanta airportsAlso issued as an M.S. thesis, Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1972Includes bibliographical referencesDuring the month of January, a survey was conducted at Boston and Atlanta Airports to obtain input data for an interactive computer simulation of runway and taxiway traffic being developed by Lincoln Laboratory. Data was collected for landings, takeoffs, and taxiing; included were such items as runway occupancy times, touchdown distances and times, liftoff distances and times, time over a given taxiway stretch, taxiway intersection delays and pre-takeoff delays. This thesis presents the results of the analysis of that data. Sample means and deviations of various parameters are given. The results of further analysis, intended to disclose inherent patterns in the data, are also discussed. First, it was found that there were few statistically significant differences in the speeds of different aircraft over the same taxiway stretch, regardless of the aircraft type or direction of travel. Also, length of the segment did not seem to have a uniform effect on speed. It is felt, though, that the location of the segment does have a substantial influence on taxiing speed. Secondly, touchdown distance was not significantly different on runways equipped with VASI (Visual Approach Slope Indicator) systems, when compared with non-VASI runways. Both exhibit substantial variance in the distribution of touchdown points. - 3 - However, the distribution for VASI-runways presents a double peaking not otherwise noticed, which may indicate a difference between a VASI-assisted and an unguided landing. Third, in analyzing runway occupancy times, it was found that the time to a given exit did not statistically vary, in general, regardless of the aircraft type involved. Overall differences between types were noted, with average occupancy times increasing with weight, but this is seen as being caused mainly by different patterns of exit use. On takeoffs, very few differences in occupancy times were found, regardless of type or runway. Lastly, other analyses which could be performed on the collected data are discussed, and suggestions are made for the planning of future surveys. In particular, a more automated data gathering system, involving remote sensors on the runway, is strongly recommended for greater accuracy

ANALYZING THE RUNWAY CAPACITY OF COMPLEX AIRPORTS

This paper describes a simulation modeling system we have developed, called Airport Capacity Analysis Through Simulation (ACATS). Airport capacity, in the sense of the average throughput obtainable during periods of high demand, is determined directly by simulating a constant flow of arrivals and departures for hundreds of hours. The user interface for ACATS provides a fast way to set up the elements of the airport that are essential for calculating runway capacity. It also supports the use of Air Traffic Control (ATC) separation rules that may become feasible as technology improves. The software in the user interface automatically converts the data for any airport into a standardized set of files that are then processed by the ACATS simulation software. At the core of the ACATS software is a simulation engine that is common to all airport analyses. That means that the simulation is driven by data representing the ATC rules, runway layout, and demand characteristics. The output of ACATS includes an animation of the simulation, statistics about the observed throughput, and a set of graphical analysis charts. The animation and graphical results produced by ACATS are important tools in explaining the analysis to the end user and in validating the results of the simulation. This paper will describe 1) the ACATS user interface tool that permits the user to easily describe the problem, 2) the ACATS simulation module, and 3) the methodology that governs the ACATS algorithms

Restrictions on Competition in Municipal Competitive Procurement in Sweden

The bidding process in public procurement in Sweden is a first-price sealed bid auction. Although there is a competitive effect on the bids in this type of auction, the contracting entity can, through the choice of procurement procedure, restrict the number of bidders. This paper studies this choice and imposes an implementation cost on the contracting entity to motivate such a restriction. The results, based on data for Swedish municipalities, suggest that contract specifications and municipality characteristics (that are assumed to influence the implementation cost) affect the volume of the procurement and the number of bidders but not necessarily the choice of procurement procedure. Copyright International Atlantic Economic Society 2005D44, H57, K20,

Peer selection and influence of delinquent behavior of immigrant and nonimmigrant youths: Does context matter?

Item does not contain fulltexthis study examines selection and influence related to delinquent behaviors of immigrant and nonimmigrant adolescents attending three majority-immigrant schools (54% to 65.2% immigrant) and four minority-immigrant schools (11.1% to 25.1% immigrant) in one community. The sample included 1,169 youths (50.4% male; 24.2% immigrant) initially between the ages of 12 and 16 years (M =13.92, SD = 0.85). Results showed that immigrant and nonimmigrant adolescents were similar to their peers on delinquent behaviors, and peer selection and social influence operated in a complementary manner to explain this similarity. The processes did not differ between immigrants and nonimmigrants or between school contexts, suggesting that immigrants do not differ from nonimmigrants on either the prevalence or the processes behind delinquency

Multiple early factors anticipate post-acute COVID-19 sequelae.

Post-acute sequelae of COVID-19 (PASC) represent an emerging global crisis. However, quantifiable risk factors for PASC and their biological associations are poorly resolved. We executed a deep multi-omic, longitudinal investigation of 309 COVID-19 patients from initial diagnosis to convalescence (2-3 months later), integrated with clinical data and patient-reported symptoms. We resolved four PASC-anticipating risk factors at the time of initial COVID-19 diagnosis: type 2 diabetes, SARS-CoV-2 RNAemia, Epstein-Barr virus viremia, and specific auto-antibodies. In patients with gastrointestinal PASC, SARS-CoV-2-specific and CMV-specific CD8+ T cells exhibited unique dynamics during recovery from COVID-19. Analysis of symptom-associated immunological signatures revealed coordinated immunity polarization into four endotypes, exhibiting divergent acute severity and PASC. We find that immunological associations between PASC factors diminish over time, leading to distinct convalescent immune states. Detectability of most PASC factors at COVID-19 diagnosis emphasizes the importance of early disease measurements for understanding emergent chronic conditions and suggests PASC treatment strategies