Corridor Structure Research Articles

Corridor navigation of the mobile robot using image based control

In this paper, the wall following navigation algorithm of the mobile robot using a mono vision system is described. The key points of the mobile robot navigation system are effective acquisition of the environmental information and fast recognition of the robot position. Also, from this information, the mobile robot should be appropriately controlled to follow a desired path. For the recognition of the relative position and orientation of the robot to the wall, the features of the corridor structure are extracted using the mono vision system, then the relative position, the offset distance and steering angle of the robot from the wall, is derived for a simple corridor geometry. For the alleviation of the computation burden of the image processing, the Kalman filter is used to reduce search region in the image space for line detection. Next, the robot is controlled by this information to follow the desired path. The wall following control scheme by the PD control scheme is composed of two control parts, the approaching control and the orientation control, and each control is performed by steering and forward-driving motion of the robot. To verify the effectiveness of the proposed algorithm, the real time navigation experiments are performed. Through the result of the experiments, the effectiveness and flexibility of the suggested algorithm are verified in comparison with a pure encoder-guided mobile robot navigation system.

Quantifying Spatial Characteristics for Travel Behavior Models

Land use initiatives represent a potentially effective tool for coping with the kinds of mobility patterns that North American cities face in the 1990s and in the coming century. As fine-grained data about land use and travel activity become available, they provide the opportunity to improve the understanding of the linkage between land use and transportation. The neighborhood characteristics that could affect travel behavior on the non-work tour are examined in detail. Neighborhood characteristics include land use, network, and accessibility-related characteristics quantified through the use of a geographic information system. Ultimately, such measures could be used in conjunction with detailed surveys of travel behavior to specify, calibrate, and use models of modal choice and trip type that are more sensitive to the fine-grained spatial structure of neighborhoods and transportation corridors in metropolitan areas. Microlevel data for the Boston metropolitan area, together with a 1991 activity survey of approximately 10,000 residents, provide a rich empirical basis for experimenting with relevant neighborhood measures and for simulating their effects on travel behavior. Spatial characteristics affect travel behavior even on the relatively (spatially) restricted nonwork tour and could be potentially useful for transportation planning.

Can biological assessments discriminate among types of stress? A case study from the Eastern Corn Belt Plains ecoregion

AbstractWe investigated the feasibility of using the structure of fish and benthic macroinvertebrate communities to distinguish among major types of stressors (e.g., siltation, nutrient enrichment, and stream structural degradation) using spatially and temporally matched data on stressors and responses. The 19 stressor variables addressed stream chemistry and in‐stream habitat and included biological oxygen demand (BOD), total suspended solids, nitrogen, phosphorus, and components of the Qualitative Habitat Evaluation Index. The 42 response variables addressed fish and invertebrate community structure and included many of the component metrics of the Index of Biological Integrity and the Invertebrate Community Index as well as variables specifically calculated for this project. All data were collected between 1988 and 1994 by the Ohio Environmental Protection Agency in the Eastern Corn Belt Plains ecoregion. Prior to analysis, variables were transformed to near normality, and variables significantly correlated with drainage area were fit to regression models and the resulting residuals used in the analyses. Multivariate analyses included factor and discriminant analysis. The first six stressor factors explained 69% of the variation. Discriminant functions formed using the response variables significantly separated site clusters classified into high, medium, and low categories along stressor gradients. Both fish and macroinvertebrate variables were important in distinguishing site categories. For example, percentage Tanytarsini midges and percentage Glyptotendipes were important in distinguishing sites having high and low BOD. Percentage darters was associated with sites having high scores for stream corridor structure and low concentrations of inorganic nutrients, and percentage round‐bodied suckers was associated with sites having low BOD and low concentrations of zinc and lead. These results indicate that diagnostic models may be developed that will be useful for site‐specific and regional assessments.

Seismic structure of the upper mantle in a central Pacific corridor

The seismic structure of the Tonga‐Hawaii corridor has been investigated by combining two data sets: Revenaugh and Jordan's reflectivity profile from ScS reverberations, which provides travel times to and impedance contrasts across the major mantle discontinuities, and 1500 new observations of frequency‐dependent phase delays for the three‐component S, SS, and SSS body waves and the R1 and G1 surface waves, which constrain the velocity structure within this layered framework. The shear waves turning in the upper mantle showed significant splitting of the SH and SV components, indicative of shallow polarization anisotropy. The data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric, radially anisotropic structure. The final model, PA5, is characterized by a high‐velocity, anisotropic lid, bounded at 68 km depth by a large (negative) G discontinuity; a low‐velocity, anisotropic layer below G, extending to a small L discontinuity at 166 km; an isotropic, steep‐gradient region between 166 km and 415 km; and transition‐zone discontinuities at 415, 507, and 651 km. The depth of the radial anisotropy in PA5 is shallower than in most previous studies based on surface waves and higher modes. The average value of radial shear anisotropy in the lid, +3.7%, is consistent with the magnitude expected from the spreading‐controlled models of olivine orientation, while anisotropy in the low‐velocity zone, which is required by our data set, could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present‐day plate motions. On the basis of recent work by Hirth and Kohlstedt, we suggest that the G discontinuity is caused by a rapid increase in the water content of mantle minerals with depth, marking the fossilized lower boundary of the melt separation zone active during crust formation. The high‐gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval. The average shear‐velocity gradient in the transition zone is lower than in most previous seismic models, in better agreement with the predictions for a pyrolitic composition.

Invasibility of Species‐Rich Communities in Riparian Zones

Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lockout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hoh drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and to the physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested.

Implications of altitudinal migration for conservation strategies to protect tropical biodiversity: a case study of the Resplendent QuetzalPharomacrus mocinnoat Monteverde, Costa Rica

SummaryWe documented habitat use by the Resplendent QuetzalPharomacrus mocinno, a large frugivorous bird that breeds in cloud-forests in the highlands of Central America, to assess the adequacy of protection afforded to regional biodiversity by the Monteverde reserve complex, a protected natural area that includes most of the highland forests of the Tilarán mountain range in western Costa Rica. Our results demonstrated that this relatively large (20,000 ha) protected natural area does not adequately protect the area's biodiversity. Through the use of radio-telemetry, we identified the areas on the Pacific slopes that are most critical to altirudinally migrating Quetzals. These forest patches are subject to deforestation and degradation and are rapidly becoming further isolated from other remaining forest. The possibility of the local extirpation of the Quetzal, through continued habitat loss on the Pacific slopes, presents an unusual dilemma for the region because the species is the major attraction for the Ideal tourist industry which now includes over 80 businesses and annually generates over US$5 million in local revenue. Therefore, its extirpation would seriously affect regional economic stability. In order to protect the Monteverde Quetzal population, we propose a regional conservation plan that depends on participation of local landowners to protect their remaining forest fragments and allows for the development of corridors to connect critical habitats as the focus of a regional conservation effort. While the ecological significance of the structure of corridors per se, versus other possible formats, is still being debated, we have selected the corridor format primarily because it is relatively easy for landowners to grasp the concept and the necessity for continuity of the corridor network. This recognition provides an important incentive for participation across property boundaries, promoting cooperation in a group effort rather than as isolated actions. Success of this cooperative plan will provide an example for grass-roots participation in buffer-zone management strategies elsewhere in the Neotropics.

Planning for an extensive open space system: linking landscape structure and function

Open space is a term used by landscape planners and landscape architects for land areas that are intentionally left unbuilt as fields and forests while the land around them is developed into buildings and pavement. When rural forested landscapes are developed, open space typically assumes a changed structure of remnant corridors, nodes, and patches of the pre-existing forest landscape matrix. The spatial configuration of these remnant open spaces typically reflects a response to land use controls and accidents of property boundary locations, rather than a concern for landscape structure and function. Landscape structure describes the spatial configuration of the open and developed elements of the landscape at various scales. Landscape function describes the flow of nutrients, species, and energy between these elements. This paper presents a strategy for planning the conception, implementation and management of an extensive open space system for a rural Massachusetts landscape based on key landscape ecological principles which recognize the importance of spatial configuration and the role of connectivity. This open space system is proposed as a key component of a sustainable landscape in which the future integrity of the landscape is guided by contemporary land use policies and practices. The system is ideally comprised of public and privately owned open space lands aggregated into a network that supports the maintenance and enhancement of landscape functions. It differs from most prior open space planning programs in the US in several respects: it is conceived at the landscape scale and addresses the importance of inter-scale connections, it is based on assessment procedures that link structure and function, and it recognizes both the positive (restorative) and negative role of human-induced change and disturbance in the landscape.