where A represents the magnetic vector potential, is an integral of the hydromagnetic equations. This -integral made it possible to formulate a variational principle for the force-free magnetic fields. The integral expresses the fact that motions cannot transform a given field in an entirely arbitrary different field, if the conductivity of the medium isconsidered infinite. In this paper we shall show that the full set of hydromagnetic equations admit five more integrals, besides the energy integral, if dissipative processes are absent. These integrals, as we shall presently verify, are I2 =fbHvdV, (2)

Proceedings of the National Academy of Sciences

생체의 모델링과 Simulation

Safety is emerging as an area of increased attention and awareness within transportation engineering. Historically, the safety of new and innovative traffic treatments has been difficult to assess, primarily because of a lack of good predictive models of crash potential and a lack of consensus on what constitutes a safe or unsafe facility. An FHWA-sponsored research project investigated the potential to derive surrogate measures of safety from existing traffic simulation models. These surrogate measures could then be used to support evaluations of various traffic engineering alternatives, including facilities that have not yet been built and strategies that have not yet been used. Each surrogate measure is collected on the basis of the occurrence of a conflict event, which is an interaction between two vehicles in which one vehicle must take evasive action to avoid a collision. The surrogate measures that are proposed as the best are time to collision, postencroachment time, deceleration rate, maximum spe...

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Surrogate safety measures from traffic simulation models

The agent computing paradigm is rapidly emerging as one of the powerful technologies for the development of large-scale distributed systems to deal with the uncertainty in a dynamic environment. The domain of traffic and transportation systems is well suited for an agent-based approach because transportation systems are usually geographically distributed in dynamic changing environments. Our literature survey shows that the techniques and methods resulting from the field of agent and multiagent systems have been applied to many aspects of traffic and transportation systems, including modeling and simulation, dynamic routing and congestion management, and intelligent traffic control. This paper examines an agent-based approach and its applications in different modes of transportation, including roadway, railway, and air transportation. This paper also addresses some critical issues in developing agent-based traffic control and management systems, such as interoperability, flexibility, and extendibility. Finally, several future research directions toward the successful deployment of agent technology in traffic and transportation systems are discussed.

A Review of the Applications of Agent Technology in Traffic and Transportation Systems

This paper presents a new method for constructing quickly and automatically precision tree models from point clouds of the trunk and branches obtained by terrestrial laser scanning. The input of the method is a point cloud of a single tree scanned from multiple positions. The surface of the visible parts of the tree is robustly reconstructed by making a flexible cylinder model of the tree. The thorough quantitative model records also the topological branching structure. In this paper, every major step of the whole model reconstruction process, from the input to the finished model, is presented in detail. The model is constructed by a local approach in which the point cloud is covered with small sets corresponding to connected surface patches in the tree surface. The neighbor-relations and geometrical properties of these cover sets are used to reconstruct the details of the tree and, step by step, the whole tree. The point cloud and the sets are segmented into branches, after which the branches are modeled as collections of cylinders. From the model, the branching structure and size properties, such as volume and branch size distributions, for the whole tree or some of its parts, can be approximated. The approach is validated using both measured and modeled terrestrial laser scanner data from real trees and detailed 3D models. The results show that the method allows an easy extraction of various tree attributes from terrestrial or mobile laser scanning point clouds.

Fast Automatic Precision Tree Models from Terrestrial Laser Scanner Data

In this paper a traffic signal control system based on real-time simulation, multi-agent control scheme, and fuzzy inference is presented. This system called HUTSIG is closely related to the microscopic traffic simulator HUTSIM, both have been developed by the Helsinki University of Technology. The HUTSIM simulation model is used both for off-line evaluation of the signal control scheme and for on-line modeling of traffic situations during actual control. Indicators are derived from the simulation model as input to the control scheme. In the presented control technique, each signal operates individually as an agent, negotiating with other signals about the control strategy. Here the decision making of the agents is based on fuzzy inference that allows a combination of various aspects like fluency, economy, environment and safety. The fuzzy implementation of the HUTSIG signal control system is developed under the FUSICO-project at Helsinki University of Technology.

Multi-Agent Fuzzy Signal Control Based on Real-Time Simulation

The Finnish Geodetic Institute has been developing a mobile road environment mapping system, named as ROAMER, since 2003. The vehicle-borne ROAMER system consists of a carrying platform, positioning and navigation systems, and a 3D data acquisition system. The system employed a 3D laser scanner operated in a profiling mode. The laser scanner can be mounted in several different positions to meet the special needs of some planned applications of the mobile mapping system. In order to be able to accomplish the high automation in 3D modeling, a laser scanner capable to provide dense point clouds was set as the requirement for the system. Additionally, the system is aimed to be a flexible moving laboratory for various road environment applications. The wide field of view and a high point measurement frequency of 120 kHz provided by the laser scanner in use, makes the ROAMER unique. This paper describes the hardware and the navigation solution of the FGI ROAMER. We also discuss the applicability of mobile mapping system in the field of traffic engineering as data source. There is a wide range of laser sensors applicable, as the MMS presented in this paper, but also static laser profilers could be used for real-time traffic flow measurements. This data could be used as input to the MMS based 3D virtual models of the different traffic places to help traffic planners to increase the traffic safety. The detailed 3D models of the transport systems can be used for traffic modeling and traffic simulation systems. In 3D models the interactions between vehicles, pedestrians and bicycles can be examined in high detail. Also the interaction with traffic environment can be studied.

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Road environment mapping system of the finnish geodetic institute - fgi roamer -

The problems with urban city traffic are getting worse, because of increasing traffic demand. Also the traffic environment and control systems are getting more and more complex. Transport telematics may offer new solutions, but it is difficult to predict its impact. Hence there is a need for new tools for traffic planning and research as well as for development of new traffic control strategies. The new tool has to be able to model all the essential interactions of the traffic process in sufficient detail. The subject of this thesis is the development of a general urban traffic simulator. The overall aim has been to develop a versatile planning and research tool for detailed examination of the traffic process and its interactions. With a simulator it is possible to examine the traffic system in a controlled way and without disturbing the actual traffic. Numerous different alternatives can be tested in order to choose the most suitable one. For evaluation the simulator produces various measures that indicate the efficiency, safety and emissions of the traffic. The animation provided by the simulation is very useful in demonstrating different alternatives to decision makers and for the general public. HUTSIM has been developed by the Helsinki University of Technology, Laboratory of Transportation Engineering since 1989. HUTSIM was originally developed for evaluation of signal control, but has since evolved towards more general urban traffic and control simulation. This thesis is the continuation to the author's licentiate thesis on HUTSIM as a traffic signal simulator, opening new perspectives for applications based on the HUTSIM simulation. The flexible and versatile object-oriented modeling has made HUTSIM easy to adapt for most various simulation studies. HUTSIM's rule-based vehicle dynamics produces a consistent and stable driving behavior in any traffic situation with only a set of few rules for speed control, lane changing and gap acceptance. The parameters of this rule system has been calibrated by many field studies. The driving dynamics has been adapted to cover not only street traffic but the freeway environment, too. HUTSIM also offers multi-modal capabilities like pedestrian traffic and public transport simulation. An open and generic driver modeling framework is outlined in this thesis.

Hutsim - urban traffic simulation and control model: principles and applications

http://kth.diva-portal.org/smash/get/diva2:1205227/FULLTEXT01

An intelligent control system for traffic lights with simulation-based evaluation

The vehicle-based laser scanning (VLS, also known as mobile mapping) is a new technology, which is currently under development for creating 3D models of the surrounding environment. VLS is based on the integration of GPS, IMU, laser scanner and preferably digital cameras mounted on top of a moving platform, i.e. a car in most applications. VLS is a logical development after the first operative Airborne Laser Scanner (ALS) in 1994 and Terrestrial Laser Scanners mounted on top of a tripod. The data/image processing of VLS are mainly based on modifications of the methods created for ALS and TLS taking into account the differences of VLS compared to ALS and TLS. Compared to ALS, the geometry of VLS scanning is different and the pulse density varies as function of range. Two main differences between stationary TLS and constantly moving VLS are the evenness of the data and the perspective. In VLS, the point cloud is evenly distributed along the driving direction, and the viewing direction to the target remains constant. In the stop-and-go mode, the data characteristics of the VLS and conventional TLS are similar. A reasonable amount of research has been done to develop methods for single-time VLS processing, but there have not been any attempts to our knowledge of multitemporal processing of VLS data. In this paper, the high potential of change detection based on multitemporal VLS point clouds was demonstrated. Example cases include the change detection of city models and defoliation of city trees. A method to map biomass and biomass change of (city) trees was developed.

Iisakki Kosonen

Papers

Multi-Agent Fuzzy Signal Control Based on Real-Time Simulation

Road environment mapping system of the finnish geodetic institute - fgi roamer -

Hutsim - urban traffic simulation and control model: principles and applications

An intelligent control system for traffic lights with simulation-based evaluation

Map updating and change detection using vehicle-based laser scanning