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Road Network (road + network)
Selected AbstractsAdaptive Zooming in Web CartographyCOMPUTER GRAPHICS FORUM, Issue 4 2002Alesandro Cecconi Abstract Beyond any doubt much of the current web mapping and web GIS applications lack cartographic quality. Thereasons aren't only the technical limitations related to Internet delivery, but also the neglect of one of the maincartographic principles of digital mapping, namely adaptive zooming. Adaptive zooming describes the adjustmentof a map, its contents and the symbolization to target scale in consequence of a zooming operation. The approachdescribed in this paper proposes the combination of two commonly known concepts: on the one hand levelsof detail (LoD) for those object classes, that require high computational cost for the automated generalizationprocess (e.g. buildings, road network); on the other hand an on-the-fly generalization for those object classeswhich can be generalized by less complex methods and algorithms (e.g. rivers, lakes). Realizing such interactiveand dynamic concept for web mapping requires the use of vector based visualization tools. The data format bestmeeting the criteria is the W3C standard Scalable Vector Graphics (SVG). Thus, it has been used to implementthe presented ideas in a prototype application for topographic web mapping based on the landscape modelVECTOR25 of the Swiss Federal Office of Topography. [source] Hybrid Meta-Heuristic Algorithm for the Simultaneous Optimization of the O,D Trip Matrix EstimationCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2004Antony Stathopoulos These include a genetic algorithm (GA), a simulated annealing (SA) algorithm, and a hybrid algorithm (GASA) based on the combination of GA and SA. The computational performance of the three algorithms is evaluated and compared by implementing them on a realistic urban road network. The results of the simulation tests demonstrate that SA and GASA produce a more accurate final solution than GA, whereas GASA shows a superior convergence rate, that is, faster improvement from the initial solution, in comparison to SA and GA. In addition, GASA produces a final solution that is more robust and less dependent on the initial demand pattern, in comparison to that obtained from a greedy search algorithm. [source] Zygomatic complex fractures in a suburban Nigerian populationDENTAL TRAUMATOLOGY, Issue 2 2005Vincent Ugboko Abstract,,, A retrospective analysis of 128 zygomatic complex fractures was undertaken. There were 109 males (85.2%) and 19 females (14.8%), aged 3,74 years (mean ± SD, 33 ± 12.6 years). Patients in the third decade of life (38.3%) recorded the highest incidence. Road traffic accidents (74.2%) mainly from automobile (61.7%) and motorcycle (9.4%) involvement were the predominant etiology. While 38.8% of them presented within the first 24 h, males were relatively earlier than their female counterparts, although this was not statistically significant (P > 0.05). Class 3 fractures were the commonest (50%), followed by classes 2 (zygomatic arch) and 4, respectively. Most class 6 fractures (6.3%) resulted from gunshot injuries. There were 116 unilateral (left 63, right 53) and 12 bilateral fractures with the right side of the face recording more zygomatic arch fractures. In addition, statistical significance was observed between etiology, class and type of fracture (P < 0.05). One hundred and twenty-four (136 fractures) patients were available for treatment as four declined. Twelve cases did not require treatment while others were managed by either closed or open reduction under general anesthesia. Gillies' temporal approach was the commonest (57.1%) surgical technique employed. However the unstable nature of the fractures necessitated open reduction and transosseous wiring in 33 cases. The high prevalence of zygomatic complex fractures arising from vehicular accidents reflects the poor status of the road network in rural and suburban Nigerian communities. Hence government should improve on existing infrastructures, decongest the highways and enforce traffic laws amongst road users. In addition, the need to encourage massive investments in safer alternative transport systems is emphasized. [source] Persistence of road runoff generation in a logged catchment in Peninsular MalaysiaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2007Alan D. Ziegler Abstract Measurements of saturated hydraulic conductivity (Ks) and diagnostic model simulations show that all types of logging road/trail in the 14·4 ha Bukit Tarek Experimental Catchment 3 (BTEC3) generate substantial Horton overland flow (HOF) during most storms, regardless of design and level of trafficking. Near-surface Ks(0,0·05 m) on the main logging road, skid trails and newly constructed logging terraces was less than 1, 2 and 34 mm h,1, respectively. Near-surface Ks on an abandoned skid trail in an adjacent basin was higher (62 mm h,1), owing to the development of a thin organic-rich layer on the running surface over the past 40 years. Saturated hydraulic conductivity measured at 0·25 m below the surface of all roads was not different (all <6 mm h,1) and corresponded to the Ks of the adjacent hillslope subsoil, as most roads were excavated into the regolith more than 0·5,1 m. After 40 years, only limited recovery in near-surface Ks occurred on the abandoned skid trail. This road generated HOF after the storage capacity of the upper near-surface layer was exceeded during events larger than about 20 mm. Thus, excavation into low- Ks substrate had a greater influence on the persistence of surface runoff production than did surface compaction by machinery during construction and subsequent use during logging operations. Overland flow on BTEC3 roads was also augmented by the interception of shallow subsurface flow traveling along the soil,saprolite/bedrock interface and return flow emerging from the cutbank through shallow biogenic pipes. The most feasible strategy for reducing long-term road-related impacts in BTEC3 is limiting the depth of excavation and designing a more efficient road network, including minimizing the length and connectivity of roads and skid trails. Copyright © 2007 John Wiley & Sons, Ltd. [source] Big diameter tunnelling beneath low rock cover.GEOMECHANICS AND TUNNELLING, Issue 3 2009Bau eines Großtunnels unter geringer Felsüberdeckung Abstract The Clem Jones Tunnel (former North-South Bypass Tunnel) is the first project to get underway as part of Brisbane's transport plan which aims to improve the urban road network. The total length to be excavated is 6.8 km which includes 4.8 km of driven tunnel and associated road connections. Construction commenced in August 2006 with project completion targeted well before the contractual completion date of October 2010. Due to the local geology, in particular the hard Brisbane tuff and Neranleigh-Fernvale formation a combination of tunnel excavation methods are used. The majority of the tunnel is excavated by two tunnel boring machines in rock having a compressive strength of between 80 and 150 MPa. Ten roadheaders are excavating the remaining tunnels such as ramps, access tunnels, cross passages and merges. A major challenge arose during the planning of the initial mainline excavation underneath the Royal National Association Showground in Bowen Hills. This section contains low rock cover and historical maps indicate that the Showground is located within a former topographic depression (alluvial valley) where a creek once flowed through. Due to traffic merge design requirements, both TBM and roadheader excavation methods were required to be used in this challenging geological profile. The answer was to stabilise the alluvium above both TBM section tunnels from the surface prior to excavation and to operate the TBM in single shield mode with immediate grouting of annular void from the tail shield. In addition, the roadheader section of tunnel required additional support by spiles and canopy tubes installed from the tunnel face. Der Clem Jones Tunnel (ehemals North South Bypass Tunnel) ist das erste in Angriff genommene Projekt des Brisbane-Transportplans. Dieser Plan hat das Ziel, das städtische Straßennetzwerk zu verbessern. Insgesamt wird eine Strecke von 6,8 km aufgefahren, einschließlich 4,8 km bergmännische Tunnel und zugehörige Straßenanbindungen. Die Bauarbeiten begannen im August 2006, und die Fertigstellung des Projekts ist deutlich vor dem vertraglich vereinbarten Fertigstellungstermin im Oktober 2010 geplant. Der größte Teil der Tunnel wird durch zwei Tunnelbohrmaschinen im Hartgestein mit einer Druckfestigkeit zwischen 80 und 150 MPa ausgebrochen. Zehn Teilschnittmaschinen fahren die übrigen Tunnel wie Rampen, Zugangstunnel, Querschläge und Verbindungen auf. Eine große Herausforderung ergab sich während der Planung des Haupttunnelvortriebs unter dem Ausstellungsgelände der Royal National Association in Bowen Hills. Dieses Gebiet besitzt eine geringe Felsüberdeckung, und aus historischen Karten weiß man, dass das Ausstellungsgelände in einer ehemaligen topografischen Senke (alluviales Tal) liegt, durch die früher ein Bach floss. Aufgrund von Verkehrsplanungsanforderungen war es notwendig, sowohl Tunnelbohrmaschinen als auch Teilschnittmaschinen in dieser schwierigen geologischen Situation zu verwenden. Die Lösung bestand darin, das Schwemmland über beiden TBMTunneln von oben her zu stabilisieren und die Tunnelbohrmaschine in der Einfachschildbetriebsart zu fahren, wobei der Ringspalt vom Schildschwanz aus verpresst wird. Die durch Teilschnittmaschinen ausgebrochenen Tunnel mussten außerdem zusätzlich durch Spieße und eine Rohrschirmsicherung gestützt werden. [source] Catchment-scale contribution of forest roads to stream exports of sediment, phosphorus and nitrogenHYDROLOGICAL PROCESSES, Issue 23 2007Gary J. Sheridan Abstract The relative contribution of forest roads to total catchment exports of suspended sediment, phosphorus, and nitrogen was estimated for a 13 451 ha forested catchment in southeastern Australia. Instrumentation was installed for 1 year to quantify total in-stream exports of suspended sediment, phosphorus, and nitrogen. In addition, a total of 101 road,stream crossings were mapped and characterized in detail within the catchment to identify the properties of the road section where the road network and the stream network intersect. Sediment and nutrient generation rates from different forest road types within the catchment were quantified using permanent instrumentation and rainfall simulation. Sediment and nutrient generation rates, mapped stream crossing information, traffic data and annual rainfall data were used to estimate annual loads of sediment, phosphorus, and nitrogen from each stream crossing in the catchment. The annual sum of these loads was compared with the measured total catchment exports to estimate the proportional contribution of loads from roads within the catchment. The results indicated that 3·15 ha of near-stream unsealed road surface with an average slope of 8·4% delivered an estimated 50 t of the 1142 t of total suspended sediment exported from the catchment, or about 4·4% of the total sediment load from the forest. Stream discharge over this period was 69 573 Ml. The unsealed road network delivered an estimated maximum of 22 kg of the 1244 kg of total phosphorus from the catchment, or less than 1·8% of the total load from the forest. The average sediment and phosphorous load per crossing was estimated at 0·5 t (standard deviation 1·0 t) and 0·22 kg (standard deviation 0·30 kg) respectively. The lower proportional contribution of total phosphorus resulted from a low ratio of total phosphorus to total suspended sediment for the road-derived sediment. The unsealed road network delivered approximately 33 kg of the 20 163 kg of total nitrogen, about 0·16% of the total load of nitrogen from the forest. The data indicate that, in this catchment, improvement of stream crossings would yield only small benefits in terms of net catchment exports of total suspended sediment and total phosphorus, and no benefit in terms of total nitrogen. These results are for a catchment with minimal road-related mass movement, and extrapolation of these findings to the broader forested estate requires further research. Copyright © 2007 John Wiley & Sons, Ltd. [source] Short-term harvest planning including scheduling of harvest crewsINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 5 2003J. Karlsson Abstract The problem we consider is short-term harvesting planning for a total planning period of 4,6 weeks where we want to decide the harvest sequences or schedules for harvest crews. A schedule is an order or sequence of harvest areas assigned to each crew. The harvesting of areas is planned in order to meet industrial demand. The total cost includes harvesting, transportation, and storage. One considerable cost is due to the quality reduction of logs stored at harvest areas. There are a number of restrictions to be considered. Areas are of varying size and the composition of assortments in each area is different. Each harvest team has different skills, a different home base, and different production capacity. Another aspect is the road network. There is a cost related to road opening (restoring, snow removal). In this paper, we develop a mixed integer programming (MIP) model for the problem. The schedules are represented by 0/1 variables. With a limited number of schedules, the problem can be solved by a commercial MIP solver. We have also developed a heuristic solution approach that provides high-quality integer solutions within a distinct time limit to be used when more schedules are used. Computational results from a major Swedish forest company are presented. [source] Private road competition and equilibrium with traffic equilibrium constraintsJOURNAL OF ADVANCED TRANSPORTATION, Issue 1 2009Hai Yang Abstract Toll road competition is one of the important issues under a build-operate-transfer (BOT) scheme, which is being encountered nowadays in many cities. When there are two or more competing firms and each firm operates a competitive toll road, their profits are interrelated due to the competitors' choices and demand inter-dependence in the network. In this paper we develop game-theoretic approaches to the study of the road network, on which multiple toll roads are operated by competitive private firms. The strategic interactions and market equilibria among the private firms are analyzed both in determining their supply (road capacity) and price (toll level) over the network. The toll road competition problems in general traffic equilibrium networks are formulated as an equilibrium program with equilibrium constraints or bi-level variational inequalities. Heuristic solution methods are proposed and their convergences are demonstrated with simple network examples. It is shown that private pricing and competition can be both profitable and welfare-improving. [source] Thresholds in landscape connectivity and mortality risks in response to growing road networksJOURNAL OF APPLIED ECOLOGY, Issue 5 2008Jacqueline L. Frair Summary 1The ecological footprint of a road may extend for several kilometres with overlapping effects from neighbouring roads causing a nonlinear accumulation of road effects in the landscape. Availability of preferred habitat, spatial dependencies between roads and habitat types, and fidelity to traditionally used areas further confound our ability to predict population-level responses of animals to growing road networks. 2To isolate these effects, we developed an individually based movement model using elk Cervus elaphus L. as a model system. Empirically derived movement rules redistributed elk under different amounts of preferred habitat (clearcuts), road densities, and road development schemes. We tracked potential mortality risk (given time spent near roads) and emigration rates (given declining accessibility of foraging habitat). 3Design of the road network accounted for up to 30,55% difference in mortality risk and emigration rates, with the largest differences occurring at intermediate road densities (1,1·5 km km,2) when road effects began to saturate the landscape. Maintaining roads in association with clearcuts caused a decline in habitat accessibility equivalent to replacing 50,75% of these foraging patches with conifer forest. A nine-fold difference in potential emigration was observed after varying elk tolerance for declining habitat accessibility despite holding local movement biases constant. 4Elk responses to growing road networks were non-linear, exposing thresholds for road density that were reflected in the home range occupancy patterns of a large sample of elk in the region. 5Synthesis and applications. Our approach provides a means of scaling-up complex movement decisions to population-level redistribution, separating the confounding effects of landscape context from road effects, and exposing thresholds in connectivity and mortality risks for wildlife caused by infrastructure growth. Our model indicated that road densities , 0·5 km km,2 yielded the highest probability of elk occurrence where elk were hunted (and sensitive to roads), but disassociating roads from foraging habitats or managing human access to roads may maintain effective elk habitat at substantially higher road densities. [source] How did common ragweed (Ambrosia artemisiifolia L.) spread in Québec?JOURNAL OF BIOGEOGRAPHY, Issue 10 2007A historical analysis using herbarium records Abstract Aim, To reconstruct the spread of common ragweed (Ambrosia artemisiifolia L.; Asteraceae) using herbarium specimens to document whether the habitat preferences of this plant have shifted through time. Location, Southern Québec. Methods, Herbarium specimens stored in the main herbaria of southern Québec were used to reconstruct the spread of common ragweed. All data (sampling location, year of sampling, habitat characteristics, etc.) were incorporated into a geographical information system. Maps indicating the spatial distribution of common ragweed were produced for four time periods. The cumulative number of locations was plotted against time to construct invasion curves. The sequence of habitats where herbarium specimens were collected was also reconstructed. Results, A data base incorporating 707 common ragweed herbarium specimens was constructed for this study. The spread of common ragweed in most regions of southern Québec was initiated at the beginning of the 20th century. Herbarium specimens suggest that common ragweed first spread along river corridors. Specimens of common ragweed were not collected in agricultural fields before the mid-1920s, nor along roads and railways before the mid-1930s. The colonization of a large number of agricultural fields by common ragweed probably began with seed-contaminated crops, but was certainly accelerated by the dispersal of seeds from populations growing along nearby roads. Main conclusions, Herbarium specimens suggest that common ragweed has been present in southern Québec for at least 200 years, but the species was probably restricted to the Montréal area during the 19th century. It is likely that the development of the road network in Québec since the mid-1930s significantly contributed to the spread of common ragweed. Controlling common ragweed solely in agricultural fields would not prevent the re-infestation of crops, because roadsides would act as refuges for the weed. [source] A perception-driven autonomous urban vehicleJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2008John Leonard This paper describes the architecture and implementation of an autonomous passenger vehicle designed to navigate using locally perceived information in preference to potentially inaccurate or incomplete map data. The vehicle architecture was designed to handle the original DARPA Urban Challenge requirements of perceiving and navigating a road network with segments defined by sparse waypoints. The vehicle implementation includes many heterogeneous sensors with significant communications and computation bandwidth to capture and process high-resolution, high-rate sensor data. The output of the comprehensive environmental sensing subsystem is fed into a kinodynamic motion planning algorithm to generate all vehicle motion. The requirements of driving in lanes, three-point turns, parking, and maneuvering through obstacle fields are all generated with a unified planner. A key aspect of the planner is its use of closed-loop simulation in a rapidly exploring randomized trees algorithm, which can randomly explore the space while efficiently generating smooth trajectories in a dynamic and uncertain environment. The overall system was realized through the creation of a powerful new suite of software tools for message passing, logging, and visualization. These innovations provide a strong platform for future research in autonomous driving in global positioning system,denied and highly dynamic environments with poor a priori information. © 2008 Wiley Periodicals, Inc. [source] Highways block gene flow and cause a rapid decline in genetic diversity of desert bighorn sheepECOLOGY LETTERS, Issue 10 2005Clinton W. Epps Abstract The rapid expansion of road networks has reduced connectivity among populations of flora and fauna. The resulting isolation is assumed to increase population extinction rates, in part because of the loss of genetic diversity. However, there are few cases where loss of genetic diversity has been linked directly to roads or other barriers. We analysed the effects of such barriers on connectivity and genetic diversity of 27 populations of Ovis canadensis nelsoni (desert bighorn sheep). We used partial Mantel tests, multiple linear regression and coalescent simulations to infer changes in gene flow and diversity of nuclear and mitochondrial DNA markers. Our findings link a rapid reduction in genetic diversity (up to 15%) to as few as 40 years of anthropogenic isolation. Interstate highways, canals and developed areas, where present, have apparently eliminated gene flow. These results suggest that anthropogenic barriers constitute a severe threat to the persistence of naturally fragmented populations. [source] Empirical Analysis of a Travel-Time Forecasting ModelGEOGRAPHICAL ANALYSIS, Issue 4 2007Jinsoo You The purpose of this article is to analyze empirically a travel-time forecasting model that estimates link travel times on congested road networks. In separate studies by You and Kim, a nonparametric regression model has been developed as a core forecasting algorithm to reduce computation time and increase forecasting accuracy. In this article, the sensitivity of model parameters is evaluated so that the proposed travel-time forecasting model could be utilized in transportation information and management systems such as location-based services and intelligent transportation systems applications. [source] New centralized automatic vehicle location communications software system under GIS environmentINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2005Omar Al-Bayari Abstract Recent advances in wireless communications and networks have integrated relatively new technologies such as Global Positioning System (GPS), to the popular Global System for Mobile Communication (GSM), second generation cellular systems and the Geographic Information Systems (GIS) technologies. Automatic Vehicle Location (AVL) is based on a combination of GPS, GIS and telecommunication technologies. Automatic Vehicle Tracking systems are more and more used for different purposes, especially those related to tracking one vehicle or a fleet of vehicles. In this work, we introduce a new AVL system, which is based and developed under GIS software environment. The centralized software at the control station offers a new technology of transferring the intelligence of tracking system from the car unit, into the control office PC software. Centralized software will reduce the programming efforts in the car unit and will offer better fleet management. Moreover, the core of our system is based on the objects or the controllers of the GIS software, which reduces dramatically the overall system cost. Our system provides an easy access to change the functions of the system, with great possibility to satisfy the local needs. The design of our software will be presented with an explanation of the new supporting technologies that were to create the system. Finally, our software system has been validated using data from local road networks. Copyright © 2005 John Wiley & Sons, Ltd. [source] A risk-averse user equilibrium model for route choice problem in signal-controlled networksJOURNAL OF ADVANCED TRANSPORTATION, Issue 4 2010William H.K. Lam Abstract This paper proposes a new risk-averse user equilibrium (RAUE) model to estimate the distribution of traffic flows over road networks with taking account the effects of accident risks due to the conflicting traffic flows (left- and right-turning and through traffic flows) at signalized intersections. It is assumed in the proposed model that drivers consider simultaneously both the travel time and accident risk in their route choices. The accident risk of a route is measured by the potential accident rate on that route. The RAUE conditions are formulated as an equivalent path-based variational inequality problem which can be solved by a path-based solution algorithm. It is shown that the traditional user equilibrium (UE) model is in fact a special case of the proposed model. A numerical example on a grid network is used to illustrate the application of the proposed model and to compare the results with the conventional UE traffic assignment. Numerical results show that the traditional UE model may underestimate the total system travel time and overestimate the system accident rate. Sensitivity tests are also carried out to assess the effects of drivers' preferences, signal control parameters (i.e., green time proportions), and various network demand levels on the route choice problem. Copyright © 2010 John Wiley & Sons, Ltd. [source] Sensitivity analysis on stochastic equilibrium transportation networks using genetic algorithmJOURNAL OF ADVANCED TRANSPORTATION, Issue 3 2004Halim Ceylan Abstract This study deals with the sensitivity analysis of an equilibrium transportation networks using genetic algorithm approach and uses the bi-level iterative sensitivity algorithm. Therefore, integrated Genetic Algorithm-TRANSYT and Path Flow Estimator (GATPFE) is developed for signalized road networks for various level of perceived travel time in order to test the sensitivity of perceived travel time error in an urban stochastic road networks. Level of information provided to drivers correspondingly affects the signal timing parameters and hence the Stochastic User Equilibrium (SUE) link flows. When the information on road system is increased, the road users try to avoid conflicting links. Therefore, the stochastic equilibrium assignment concept tends to be user equilibrium. The GATPFE is used to solve the bi-level problem, where the Area Traffic Control (ATC) is the upper-level and the SUE assignment is the lower-level. The GATPFE is tested for six-junction network taken from literature. The results show that the integrated GATPFE can be applied to carry out sensitivity analysis at the equilibrium network design problems for various level of information and it simultaneously optimize the signal timings (i.e. network common cycle time, signal stage and offsets between junctions). [source] Thresholds in landscape connectivity and mortality risks in response to growing road networksJOURNAL OF APPLIED ECOLOGY, Issue 5 2008Jacqueline L. Frair Summary 1The ecological footprint of a road may extend for several kilometres with overlapping effects from neighbouring roads causing a nonlinear accumulation of road effects in the landscape. Availability of preferred habitat, spatial dependencies between roads and habitat types, and fidelity to traditionally used areas further confound our ability to predict population-level responses of animals to growing road networks. 2To isolate these effects, we developed an individually based movement model using elk Cervus elaphus L. as a model system. Empirically derived movement rules redistributed elk under different amounts of preferred habitat (clearcuts), road densities, and road development schemes. We tracked potential mortality risk (given time spent near roads) and emigration rates (given declining accessibility of foraging habitat). 3Design of the road network accounted for up to 30,55% difference in mortality risk and emigration rates, with the largest differences occurring at intermediate road densities (1,1·5 km km,2) when road effects began to saturate the landscape. Maintaining roads in association with clearcuts caused a decline in habitat accessibility equivalent to replacing 50,75% of these foraging patches with conifer forest. A nine-fold difference in potential emigration was observed after varying elk tolerance for declining habitat accessibility despite holding local movement biases constant. 4Elk responses to growing road networks were non-linear, exposing thresholds for road density that were reflected in the home range occupancy patterns of a large sample of elk in the region. 5Synthesis and applications. Our approach provides a means of scaling-up complex movement decisions to population-level redistribution, separating the confounding effects of landscape context from road effects, and exposing thresholds in connectivity and mortality risks for wildlife caused by infrastructure growth. Our model indicated that road densities , 0·5 km km,2 yielded the highest probability of elk occurrence where elk were hunted (and sensitive to roads), but disassociating roads from foraging habitats or managing human access to roads may maintain effective elk habitat at substantially higher road densities. [source] Instantaneous control for traffic flowMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 2 2007M. Herty Abstract The solution methods for optimal control problems with coupled partial differential equations as constraints are computationally costly and memory intensive; in particular for problems stated on networks, this prevents the methods from being relevant. We present instantaneous control problems for the optimization of traffic flow problems on road networks. We derive the optimality conditions, investigate the relation to the full optimal control problem and prove that certain properties of the optimal control problem carry over to the instantaneous one. We propose a solution algorithm and compare quality of the computed controls and run-times. Copyright © 2006 John Wiley & Sons, Ltd. [source] Near-shortest and K-shortest simple pathsNETWORKS: AN INTERNATIONAL JOURNAL, Issue 2 2005W. Matthew Carlyle Abstract We present a new algorithm for enumerating all near-shortest simple (loopless) s - t paths in a graph G = (V, E) with nonnegative edge lengths. Letting n = |V| and m = |E|, the time per path enumerated is O(nS(n, m)) given a user-selected shortest-path subroutine with complexity O(S(n, m)). When coupled with binary search, this algorithm solves the corresponding K -shortest paths problem (KSPR) in O(KnS(n, m)(log n+ log cmax)) time, where cmax is the largest edge length. This time complexity is inferior to some other algorithms, but the space complexity is the best available at O(m). Both algorithms are easy to describe, to implement and to extend to more general classes of graphs. In computational tests on grid and road networks, our best polynomial-time algorithm for KSPR appears to be at least an order of magnitude faster than the best algorithm from the literature. However, we devise a simpler algorithm, with exponential worst-case complexity, that is several orders of magnitude faster yet on those test problems. A minor variant on this algorithm also solves "KSPU," which is analogous to KSPR but with loops allowed. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 46(2), 98,109 2005 [source] Recommendations for Integrating Restoration Ecology and Conservation Biology in Ponderosa Pine Forests of the Southwestern United StatesRESTORATION ECOLOGY, Issue 1 2006Reed F. Noss Abstract Over the past century, ponderosa pine,dominated landscapes of the southwestern United States have been altered by human activities such as grazing, timber harvest, road building, and fire exclusion. Most forested areas within these landscapes now show increased susceptibility to stand-replacing fires, insect outbreaks, and drought-related mortality. Recent large wildfires in the region have spurred public interest in large-scale fuel reduction and restoration programs, which create perceived and real conflicts with the conservation of biodiversity. Conservation concerns include the potential for larger road networks, soil and understory disturbance, exotic plant invasion, and the removal of large trees in treated areas. Pursuing prescribed burning, thinning, or other treatments on the broad scale that many scientists and managers envision requires the reconciliation of ecological restoration with biodiversity conservation. This study presents recommendations from a workshop for integrating the principles and practices of restoration ecology and conservation biology, toward the objective of restoring the composition, structure, and function of dry ponderosa pine forests. Planning on the scale of hundreds of thousands of hectares offers opportunities to achieve multiple objectives (e.g., rare species protection and restoration of ecological structures and processes) that cannot easily be addressed on a site-by-site basis. However, restoration must be coordinated with conservation planning to achieve mutual objectives and should include strict guidelines for protection of rare, declining, and sensitive habitats and species. [source] | ||||||||||||||||||||||