Flow Corridors Research Articles

Collision risk-capacity tradeoff analysis of an en-route corridor model

Flow corridors are a new class of trajectory-based airspace which derives from the next generation air transportation system concept of operations. Reducing the airspace complexity and increasing the capacity are the main purposes of the en-route corridor. This paper analyzes the collision risk-capacity tradeoff using a combined discrete–continuous simulation method. A basic two-dimensional en-route flow corridor with performance rules is designed as the operational environment. A second-order system is established by combining the point mass model and the proportional derivative controller together to simulate the self-separation operations of the aircrafts in the corridor and the operation performance parameters from the User Manual for the Base of Aircraft Data are used in this research in order to improve the reliability. Simulation results indicate that the aircrafts can self-separate from each other efficiently by adjusting their velocities, and rationally setting the values of some variables can improve the rate and stability of the corridor with low risks of loss of separation.

Dynamic allocation and benefit assessment of NextGen flow corridors

A flow-based modeling approach is proposed to identify candidate airspace for high-density flow corridors. The input to the model is a set of projected user-preferred, wind optimal, and unconstrained 4D trajectories (4DTs). We compute Velocity Vector Fields (VVFs) in the 4D space-time and cluster the velocity vectors both in time and space to define flow of aircraft when they fly their preferred trajectories under high capacity conditions. A sliding time window is implemented to dynamically create and optimize corridors’ coordinates based on the changes in preferred trajectories. From this process we compute a NAS-wide corridor network that mimics the dynamics of user preferred trajectories. In operational setting, flights will have the option of joining a corridor that is closest to their optimal trajectory. Using NAS-wide simulation, we asses the benefit of corridor network by comparing efficiency gained by joining the corridor network against extra distance traveled to join the network. We show that much of the overall corridors benefit may be gained by creating very few corridors.

Till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams: case study of the western Canadian prairies and high plains

Complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western Canada represent the terrestrial equivalents of the trough-mouth fans of the marine palaeo-ice stream record. Intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed. First, glacier-marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time. Stacks of subglacial traction tills potentially record annual sub-marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing. Second, proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub-marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes, which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub-marginal till wedges and moraines. Glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls, resulting in the widespread development of glacitectonites and megablocks. The occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots.

Using Engagement to Negate Vigilance Decrements in the NextGen Environment

The aim of this study was to explore the extent to which increasing engagement would negate vigilance decrements in monitoring during a realistic air traffic control monitoring task. Technological advances in aircraft and navigation may change the controller's job from directing air traffic to more of a monitoring role with supervisory control. Research shows that humans are not effective monitors and can be subject to vigilance decrements. Even though vigilance decrements have been demonstrated in some settings, it is still not known if they are likely in a future ATC monitoring role. Sixteen undergraduates from the Georgia Institute of Technology trained for 6 weeks on NextSim, a medium fidelity ATC research simulator of the NextGen environment. They then performed 4 weeks of scenarios that required monitoring of flow corridors for failures of conflict evading technology. Two levels of engagement and two levels of attentional focus while monitoring were analyzed. Participants showed a significant vigilance decrement except after extended practice in the engaged condition. The findings of this study suggest that engaging the operator may alleviate the vigilance decrement, however only after practice.

NextSim: A Portable Human Factors Research Simulator for Future ATC Concepts

In this demonstration, we report on the development of a low fidelity air traffic control simulator that allows researchers to investigate human factors issues related to various NextGen concepts, like flow corridors, continuous descent arrivals, and sky-based separation. NextSim also allows the researcher to collect a number of performance, workload, and situation awareness measures.

Regulation of Brahmaputra-Jamuna River around Jamuna Bridge Site, Bangladesh: Geoenvironmental Impacts

This study is conducted to evaluate the ongoing geoenvironmental impacts of Brahmaputra-Jamuna (BJ) River around the Jamuna Bridge (JB) site which was modified prior to the construction of Jamuna Bridge in 1996. Remote sensing and GIS techniques are adopted to evaluate the temporal and spatial geohazards. This study shows that the intensity of channel shifting has been increased due to regulation of river width at Sira-jganj–Bhuiyapur section from 11 km to 4.8 km. Planform analysis shows that the major channel has been stressed to migrate (315 m/year) eastwards. The phenomena of channel changes are predicted to be the con-sequences of interaction of water flow, sedimentation and channel corridor. The erosion and deposition have complicated variations over time and space due to the abrupt changes of flow and sedimentation around the regulated section. Due to width reduction, the bridge site in the braided system acts as sluice gate which can not accommodate the entire flow to release downstream properly. The helical flow developed with the inter-action of guide bund creates local scours and helps to shift the river bank eastward.

Genetic Diversity and Population Structure of a Threatened African Tree Species,Milicia excelsa,Using Nuclear Microsatellites DNA Markers

To accurately estimate the genetic diversity and population structure for improved conservation planning ofMilicia excelsatree, 212 individuals from twelve population samples covering the species' range in Benin were surveyed at seven specific microsatellite DNA loci. All loci were variable, with the mean number of alleles per locus ranging from 5.86 to 7.69. Considerable genetic variability was detected for all populations at the seven loci (AR=4.60;HE=0.811). Moderate but statistically significant genetic differentiation was found among populations considering bothFST(0.112) andRST(0.342). All of the populations showed heterozygosity deficits in test of Hardy-Weinberg Equilibrium and significantly positiveFISvalues due to inbreeding occurring in the species. PairwiseFSTvalues were positively and significantly correlated with geographical distances (r=0.432;P=.007, Mantel's test) indicating that populations are differentiated by “isolation by distance.” Bayesian analysis of population structure showed division of the genetic variation into four clusters revealing the existence of heterogeneity in population genetic structure. Altogether, these results indicate that genetic variation inMilicia excelsais geographically structured. Information gained from this study also emphasized the need for in situ conservation of the relict populations and establishment of gene flow corridors through agroforestry systems for interconnecting these remnant populations.

Megagrooves and streamlined bedrock in NW Scotland: The role of ice streams in landscape evolution

New multibeam bathymetry data, onshore high-resolution elevation data (NEXTMap) and fieldwork in the Ullapool area of NW Scotland reveal large-scale megagrooves and streamlined bedrock forms in a well-defined ∼ 20 km wide zone. The landsystem is typical of a coherent flow corridor within a grounded ice sheet on bedrock-dominated terrain. We describe the morphology of the large-scale features, discuss their likely formation, and consider the wider implications for ice-sheet dynamics. Based on the strongly convergent bedform distribution, the presence of megagrooves and highly elongate bedrock forms, we interpret the erosional landscape to be the signature of a fast-flowing tributary that once fed the The Minch palaeo-ice stream — a major artery of the last British–Irish ice sheet. The exact genesis of bedrock megagrooves remains uncertain, although focused subglacial abrasion is likely to have carved most of the shallow, strongly parallel, features; whilst glacial meltwater may have carved or modified others. Bedform morphometry is used to discriminate zones reflecting the degree of glacial streamlining (elongation ratios < 5:1 or > 5:1). We interpret these zones to represent the transition from potentially cold-based slow ice-sheet flow to warm-based fast flow. Based on these results, and the presence of ribbed moraines, we suggest a bedform continuum model for onset zones of palaeo-ice streams on rigid beds. Rapid spatial bedform evolution is suggested to reflect an increase in subglacial erosive power that may be diagnostic of palaeo-ice-sheet thermal boundaries (i.e. from cold- to warm-based), and is also consistent with the expected downstream increase in ice velocity within an ice-stream onset zone. Finally, this study speculates on the role played by basal meltwater in ice-stream initiation and the role of ice streams and their tributaries in landscape evolution.

Residual currents and corridor of flow in the Rio de la Plata

The Rio de la Plata is a large and shallow water body that discharges onto the Atlantic Ocean. The main driving forces for the river flow are the bathymetry, tides, the outflow from the Paraná and Uruguay rivers and the winds. A numerical model covering the entire river was set up with the objective of increasing our understanding of the hydrographical features and morphological dynamics in the Estuary. The simulations revealed a counter-clockwise residual circulation in the Samborombón Bay and an eastward net flow near the Uruguayan coast. The residual flow is forced by both the tides and the bathymetry. The residence time for the entire river ranges from 40 to 80 days. However, residence times above 120 days was found in the Samborombón Bay. Three corridors of flow have been identified.

Allele variation of DYS19 and Y-Alu insertion (YAP) polymorphisms in Basques: an insight into the peopling of Europe and the Mediterranean region.

Two Y-chromosome DNA polymorphisms, the DYS19 microsatellite and the YAP (at locus DYS287), were tested in males from two autochthonous Basque populations from France and northern Navarre (Spain). The results are compared to those obtained for the same genetic markers in 32 populations from Europe, northern Africa, and western Asia. The high predominance of the DYS19*11 (190-base-pair) allele in Basques indicates that their genetic diversity for microsatellite DYS19 is around half that observed in Europeans, North Africans, and western Asians. The Y-Alu insertion (YAP+) was not detected in the Basque samples. This study attempts to throw some light on the importance of historically recent migratory movements, the main corridors of gene flow, and demographic sizes and their variations in shaping gene frequency patterns in contemporary human populations, particularly in the Mediterranean region. Historical processes may have had more significant effects on the genetic make-up of current human populations than those of prehistoric times.

A 15 yr climatology of derecho-producing mesoscale convective systems over the central and eastern United States

A 15 yr (1986-2000) climatology of derecho-producing mesoscale convective systems (DMCSs) is presented in order to better delineate their spatial and temporal patterns. Several signif- icant results emerged from the analysis, including the development of the NW flow corridor as the dominant derecho activity region in the climatology. Results suggest that, as the sample size of DMCSs increases (230 events), the prominent derecho activity corridors across the eastern US become located in the northern Plains through the Ohio Valley, with a secondary maximum in the southern Plains. Evidence further suggests that climatological factors strongly control the distribution of derechos. For example, an anomalously strong 500 hPa height gradient existed coincident with the northern US derecho activity corridor. Another aspect of derecho development is related to the temporal distribution. Evidence suggests that derecho systems tend to occur in groups or 'families', several events occurring within several days. The synoptic environment also appears to be responsi- ble for activating these corridors and providing an environment conducive to DMCS grouping.

Ice streams as the arteries of an ice sheet: their mechanics, stability and significance

Ice streams are corridors of fast ice flow (ca. 0.8 km/year) within an ice sheet and are responsible for discharging the majority of the ice and sediment within them. Consequently, like the arteries in our body, their behaviour and stability is essential to the well being of an ice sheet. Ice streams may either be constrained by topography (topographic ice streams) or by areas of slow moving ice (pure ice streams). The latter show spatial and temporal patterns of variability that may indicate a potential for instability and are therefore of particular interest. Today, pure ice streams are largely restricted to the Siple Coast of Antarctica and these ice streams have been extensively investigated over the last 20 years. This paper provides an introduction to this substantial body of research and describes the morphology, dynamics, and temporal behaviour of these contemporary ice streams, before exploring the basal conditions that exist beneath them and the mechanisms that drive the fast flow within them. The paper concludes by reviewing the potential of ice streams as unstable elements within ice sheets that may impact on the Earth's dynamic system.

Collapse dolines and deflector faults as indicators of karst flow corridors

The paper concerns collapse dolines, which appear to be one of the best-defined surface karst phenomena. Despite this appearance, one may find quite different views in the literature, and some of the aspects of their morphogenesis have been overlooked completely. Among these aspects the most obvious is the question of the ongoing development of the closed depression. Five of the most common collapse doline types found in Slovenia are considered in terms of general systems theory, leading to a conclusion that cave roof collapse remains the crucial event in a collapse doline’s development. However, the collapse event itself may be relatively subdued in terms of the volume of free fallen mass involved. Some types of collapse dolines appear along particular types of faults that function as a kind of screen; these faults are termed deflector faults. They are marked by collapsing within the caves, and by “active” collapse dolines on the surface. Existence of deflector faults is an indicator of flow corridors in the close neighbourhood.

Gene flow among habitat patches on a fragmented landscape in the spider Argiope trifasciata (Araneae: Araneidae)

The banded garden spider (Argiope trifasciata) is a common orb weaver of old field habitats in the United States. In this study, we determined levels of genetic variability and gene flow among seven populations in central Pennsylvania, based on variation at eight allozyme loci. Mean heterozygosity (observed) per population was 7. 5% and mean polymorphism was 39.3%, consistent with levels of variability in other arthropods. Values of GST for the four polymorphic loci (mean GST=0.011) suggest that gene flow prevents the genetic differentiation of these populations. The average number of migrants per generation (Nm) among these populations is estimated to be 31.3. The lack of significant interpopulation genetic differentiation among these disjunct populations may result from spiderling aerial dispersal (ballooning), a more continuous distribution of suitable habitat in the past, and perhaps the use of roadside vegetation as gene flow corridors. On the other hand, the study populations did not exhibit isolation-by-distance, suggesting that suitable habitat in our study area is experienced as less than continuous by A. trifasciata. Thus, although A. trifasciata is an excellent ballooner, ballooning does not confer unlimited access among all populations, which suggests that ballooning may be a far less effective means of long-distance dispersal than previously thought.

Geographical Variation and Gene Flow in the Eucalyptus Defoliating Beetle Chrysophtharta bimaculata (Coleoptera: Chrysomelidae)

1. Management of the eucalyptus defoliating beetle Chrysophtharta bimaculata is considered essential to the economic sustainability of timber production in Tasmanian eucalyptus plantations. This study examined population subdivision and host associations in Chrysophtharta bimaculata. We aimed to identify the spatial scale at which management practices should be implemented, and to aid in the development of long- term management strategies that avoid the build up of resistance to chemical or biological insecticides. 2. Genetic variation and gene flow among C. bimaculata subpopulations was examined using cellulose acetate gel electrophoresis. Subpopulations in central Tasmania were found to exchange relatively large numbers of immigrants, and could not be distinguished from a single large interbreeding population. 3. Restrictions to gene flow not related to geographical distance were observed among northern regional subpopulations. Our results are consistent with gene flow between northern subpopulations occurring primarily via movement into and out of central Tasmania along a limited number of gene flow corridors. We suggest that the clearing of eucalypt ash forests for agriculture in the north-west, north-east and the 'Midlands' region may be partially responsible for the restricted pattern of gene flow observed among northern sites. 4. Adjacent subpopulations collected from different hosts at three locations show no evidence of genetic differentiation. Therefore, significant regional scale population subdivision does not occur on the basis of host species. 5. That moderate to high levels of gene flow occur among beetles from all districts and hosts, implies that resistance build up is unlikely to occur if control agents are used at low levels and against a limited number of subpopulations. However, any increase in the frequency of resistant genotypes at sites where control measures have been implemented implies that resistance is being exported to all other subpopulations. This may be a particular problem in northern regional subpopulations, where reduced immigration may facilitate the local build up of resistance under a significantly less intensive control regime.

Enhancing graphical simulation output using cluster analysis

Recent work performed for the Federal Aviation Administration to support the development of future concepts of air traffic management has involved simulation modeling of patterns of airspace usage by commercial and business air traffic. The objective of these efforts has been to investigate the impacts of a pattern of airspace usage known as "free flight", whereby pilots and flight dispatchers have much more freedom to choose, say, direct or wind-optimal routing through airspace. One of the figures of merit investigated is a count of "convergence pairs" as a measure of the complexity of various traffic patterns. These are cases when aircraft in the simulation model fly close to each other. Interestingly, geographic plots of convergence pairs accumulated over time bring out certain features or patterns of congested air traffic flows or flight alignments. However, these plots are also thick with "noise" or extraneous convergence pairs, whose presence detracts from the ability to perceive congested air traffic flows. Cluster analysis has been found to be an effective method of filtering these displays so that the congested flow features are discernible. The process developed for this purpose is based on a two-pass clustering approach. The process has worked well for the simulation modeling performed to date. Classification of the locations of convergence pairs into congested flow corridors is visually appealing, and has helped distinguish differences in contrasting scenarios of airspace usage. The paper presents graphical results and describes the clustering algorithms employed.