• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1048
  • 413
  • 404
  • 156
  • 150
  • 48
  • 39
  • 39
  • 29
  • 26
  • 17
  • 14
  • 10
  • 10
  • 10
  • Tagged with
  • 2818
  • 450
  • 431
  • 366
  • 296
  • 222
  • 174
  • 172
  • 165
  • 150
  • 141
  • 140
  • 140
  • 138
  • 129
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
711

Winter Road Maintenance Planning-Decision Support Modelling

Mbiyana, Keegan January 2018 (has links)
Winter in Northern Sweden comes with very harsh and unpredictable condition associated with large amounts of snowfall covering roadways thereby affecting transportation by roads. When the road conditions i.e. the snow depth, road unevenness and friction of the road surface are accessed and found to exceed the threshold, a maintenance action must be carried out to retain the road to the required condition for the user. The aim of maintenance, in this case, is to make the road comfortable, safe and economical for the road user. Decision support system, therefore, comes in handy to facilitate on deciding what maintenance action to carry out and when the action should be carried out, where the action should be carried out and how to go about the action based on the various data and resources available. This thesis project concentrates on how to carry out a winter road maintenance after receiving an alert of an action to carry out, when to carry it out and the road network that needs to be maintained. The thesis work focusses only on two of the winter road maintenance actions namely snow ploughing of bus stops in Luleå and application of abrasives commonly referred to as sanding of bus stops. Carrying out winter road maintenance comes at a huge cost from both direct and indirect costs with the Swedish government spending about SEK 1.75 billion every year as indicated by Jana Sochor and Cecilia Yu (Sochor & Yu, 2004). This means that reduction in the maintenance cost of even 5% through optimisation of the maintenance cost would translate into a saving of about 87.5 million SEK per year and in 10 years could amount to close to 1 billion SEK. Optimization also leads to efficiency and effectiveness that could result in improved movement on the road and reduced environmental and social-economic impacts. Maintenance planning thus becomes essential for the effective and efficient execution of work and utilisation of the available scarce resource. This thesis project focusses on the use of Operations research methods to minimise the cost of carrying out a winter road maintenance action by finding the near optimal or if possible optimal solution and still deliver the required service level. The thesis delivers two main things: It first delivers a framework to support winter road maintenance decision making after an alert of an action is received and secondly an algorithm for the route that minimises the cost of maintenance by providing the route that minimises the travel distance of the ploughing/sanding vehicle from its source depot and back to the depot after completing a maintenance action assuming that the vehicle and material (fuel and sand) are in the same depot. The routes with minimum travel distance will, therefore, be that route that will reduce the labour time and in turn the labour cost, reduce the fuel consumption and the maintenance of the equipment due to reduced usage. The project uses a vehicle routing problem which is a generalised travelling Salesman as the optimisation technique to determine the optimal solution for the allocation of resources for carrying out a maintenance action to facilitate efficient utilisation of the available resources. This is with the help of a commercial optimisation software and support tools namely ArcGIS. To come up with the algorithm, the first step was a digital representation of the vehicle road network in Luleå for network analysis after which the bus stops were imported from google earth into the network. A two-stage optimisation was then carried out: first was a model for route optimisation based on the road network in ArcGIS with the objective function to minimise the travel distance and constraints based on the available resources. The results of ii the model were then exported into excel for the second optimisation for the optimal cost of maintenance done through a developed excel algorithm. The total cost of maintenance comprised direct and indirect cost. The direct cost consisted of the cost of fuel, the cost of personnel and the cost of hiring vehicles while the indirect cost results from the penalty fee charged for sanding and ploughing a bus stop after the threshold time given to a maintenance contractor by the municipality. Any bus stop that is ploughed after the threshold attracts a penalty per hour of the exceeded time. Six penalty threshold times were considered i.e. 30, 60, 90, 120, 150 and 180 minutes and a single parameter deterministic sensitivity analysis was carried out for each cost parameters to determine the sensitivity of the total maintenance cost. The more relaxed penalty thresholds were found to be less sensitive to the direct cost and the total maintenance cost compared to the more sensitive ones. When the penalty threshold is relaxed, the optimal maintenance cost reduces, and the required number of vehicles reduces. The cost of vehicle hire was found to be more sensitive than the other costs. The results of this project can help the maintenance contractor in developing a work schedule for the maintenance personnel and improve vehicle fleet management. By modelling the worst scenario, a contractor can plan for the maximum number of vehicles required and consequently the personnel required. With the optimal travel route for each vehicle and the total maintenance cost determined, maintenance contractors can determine the sustainability and profitability of their business and be able to negotiate for a better and more sustainable agreement (Contract) or for the relaxation of the penalty threshold time if it does not affect the service level required i.e. the quality and safety requirements. The approach used in this project can also be used for other winter road maintenance problems.
712

Pohybová aktivita užovky stromové v Poohří ve vztahu k silničnímu tělesu / Movement activity of Aesculapian Snake in Poohří in relation to the roadway

LAPÁČKOVÁ, Kateřina January 2015 (has links)
This thesis is focused on explaining the behaviour of population of Aesculapian Snake (Zamenis longissimus) in Poohří region related to a busy road which crosses its area of distribution. To avoid the busy road Aesculapian Snake uses the roads culverts to cross the road safely. Snakes used culverts the most often on July, when their activity culminates. One of the most used culverts was culvert Nr. 2, probably because of its proximity to man-made hatch. Snakes started their activity at 8:00 a.m. and finished at 7:00 p.m. In this study their activity culminates between 4:00 p.m. and 6:00 p.m. and by temperature between 21 - 25°C. None of adults of Aesculapian Snake was detected killed on the road. There were found only juvenile snakes of this species which weren't acquainted yet with local threats.
713

Método para análise de acidentes de trânsito com a identificação de fatores causais

Chagas, Denise Martins January 2015 (has links)
Esta tese tem como finalidade propor um método de coleta, tratamento e análise de dados de acidentes de trânsito para aplicação no Brasil. Este método tem como um de seus objetivos reconhecer os fatores que contribuem para a ocorrência dos acidentes, visto que identificar as causas dos acidentes é fundamental na busca por soluções para o problema da acidentalidade. No Brasil as bases de dados de acidentes de trânsito são, em geral, estruturadas a partir dos registros policiais e carecem de informações adequadas para a análise da segurança viária. O método proposto neste trabalho permite registrar acidentes de modo a contemplar: as características do acidente, as circunstâncias do momento, a identificação e as características dos veículos e pessoas envolvidas. Além disso, o método permite relacionar essas informações com os fatores que contribuíram para a ocorrência dos acidentes. Nesse contexto, a criação de uma base de dados de acidentes e seus fatores contribuintes, vem suprir a carência de informações essenciais para o diagnóstico e encaminhamento de soluções adequadas para os problemas motivadores dos acidentes de trânsito. A proposta desta tese está baseada em uma abordagem que combina aspectos qualitativos e quantitativos, alinhada às melhores práticas internacionais na área de segurança viária. Como resultado do desenvolvimento do método, foram elaborados instrumentos de coleta de dados contendo um formulário, um manual e procedimentos para a coleta de dados. Como resultado da aplicação prática desses instrumentos, foi criada a estrutura de uma base de dados que permitiu a definição do método proposto para a análise das causas de acidentes de trânsito. Como meio de validar o método proposto, foi realizado um estudo aplicado e são apresentadas as análises de dados dos acidentes de trânsito observados. / This thesis has the purpose of presenting a method for collecting and processing data on traffic accidents to be applied in Brazil. This method aims to acknowledge the contributor factors for the occurrence of accidents, since identifying the causes of accidents is crucial on the search for effective solutions for the road safety problem. Traffic accidents database in Brazil are generally structured based on police reports, therefore lacking adequate information for the analyses of road safety. The method proposes a registry of the accidents comprising accident characteristics, scene circumstances, vehicle as well as involved people identification and characteristics. Moreover, it allows relating that information with the accident contributory factors. In this scenery, the creation of an accident database and its contributory factors emerge to supply the lack of essential information for the diagnosis and adequate solution for traffic accidents. This thesis’ proposal has an approach that combines both quantitative and qualitative aspects, seeking to level up to the best international practice on the road safety area. As a result of the development of the method, data collection instruments were elaborated: a form, a manual, and procedures for data collection. Besides, as a result of the practical application of these instruments, a database - which allowed the definition of the method proposed for analysis of the causes of traffic accidents - was created. As a mean of validation of the method, an applied study and the data analysis of the observed traffic accidents are presented.
714

Análise das características de infraestrutura e acidentalidade viária em cruzamentos críticos da cidade de Uberlândia, MG

Souza, Paola Mundim de 27 October 2016 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Diante do aumento do número de acidentes com vítimas fatais foi definida a década de 2011 a 2020 como a Década de Ação para a Segurança Viária, o que culminou na elaboração do Plano Nacional de Redução de Acidentes e Segurança Viária, que propõe ações que estão fundamentadas em cinco pilares, um deles a infraestrutura. Este trabalho teve como objetivo analisar a influência que as características da infraestrutura exercem na segurança viária, com verificação das evoluções da incidência e severidade dos acidentes ao longo de alguns anos. Foram analisados dados de acidentes de trânsito em algumas vias da cidade de Uberlândia, MG, e as características de infraestrutura dessas vias, ou seja, qual a geometria atual e quais as mudanças implantadas nos últimos anos. Por meio do cálculo do coeficiente de Pearson foi verificada a correlação entre a variação no número de acidentes com a severidade, mudanças na infraestrutura da via e variação do fluxo veicular. De forma geral, as mudanças na infraestrutura das vias analisadas, como: aumento do número de faixas de tráfego, redução da velocidade máxima permitida, construção de viadutos e implantação de corredor estrutural fizeram com que o número de acidentes e a severidade diminuíssem. / Due to the increased number of fatal crashes, the decade from 2011 to 2020 was defined as the Decade of Road Safety, which ended in the drafting of the National Plan to Reduce Accidents and Road Safety, which proposes actions that are based on five issues, one of then the infrastructure. This thesis aimed in analyzing the influence that the infrastructure characteristics have on road safety and to check the evolution of the incidence and severity of accidents over the years. Traffic accident data were analyzed on some streets of Uberlândia, MG, and the infrastructure characteristics, that is, the current geometry and what changes were implemented in recent years. By calculating the Pearson’s coefficient, it was verified if there were a correlation between variation in the number of accidents with severity, changes in the road infrastructure, and variation of vehicular flow. In general, changes in the infrastructure of the analyzed streets, such as increased the number of lanes of traffic, reduced speed limit, construction of overpasses, and structural bus corridor deployment caused a decreasing in the number of accidents and severity. / Dissertação (Mestrado)
715

Método para análise de acidentes de trânsito com a identificação de fatores causais

Chagas, Denise Martins January 2015 (has links)
Esta tese tem como finalidade propor um método de coleta, tratamento e análise de dados de acidentes de trânsito para aplicação no Brasil. Este método tem como um de seus objetivos reconhecer os fatores que contribuem para a ocorrência dos acidentes, visto que identificar as causas dos acidentes é fundamental na busca por soluções para o problema da acidentalidade. No Brasil as bases de dados de acidentes de trânsito são, em geral, estruturadas a partir dos registros policiais e carecem de informações adequadas para a análise da segurança viária. O método proposto neste trabalho permite registrar acidentes de modo a contemplar: as características do acidente, as circunstâncias do momento, a identificação e as características dos veículos e pessoas envolvidas. Além disso, o método permite relacionar essas informações com os fatores que contribuíram para a ocorrência dos acidentes. Nesse contexto, a criação de uma base de dados de acidentes e seus fatores contribuintes, vem suprir a carência de informações essenciais para o diagnóstico e encaminhamento de soluções adequadas para os problemas motivadores dos acidentes de trânsito. A proposta desta tese está baseada em uma abordagem que combina aspectos qualitativos e quantitativos, alinhada às melhores práticas internacionais na área de segurança viária. Como resultado do desenvolvimento do método, foram elaborados instrumentos de coleta de dados contendo um formulário, um manual e procedimentos para a coleta de dados. Como resultado da aplicação prática desses instrumentos, foi criada a estrutura de uma base de dados que permitiu a definição do método proposto para a análise das causas de acidentes de trânsito. Como meio de validar o método proposto, foi realizado um estudo aplicado e são apresentadas as análises de dados dos acidentes de trânsito observados. / This thesis has the purpose of presenting a method for collecting and processing data on traffic accidents to be applied in Brazil. This method aims to acknowledge the contributor factors for the occurrence of accidents, since identifying the causes of accidents is crucial on the search for effective solutions for the road safety problem. Traffic accidents database in Brazil are generally structured based on police reports, therefore lacking adequate information for the analyses of road safety. The method proposes a registry of the accidents comprising accident characteristics, scene circumstances, vehicle as well as involved people identification and characteristics. Moreover, it allows relating that information with the accident contributory factors. In this scenery, the creation of an accident database and its contributory factors emerge to supply the lack of essential information for the diagnosis and adequate solution for traffic accidents. This thesis’ proposal has an approach that combines both quantitative and qualitative aspects, seeking to level up to the best international practice on the road safety area. As a result of the development of the method, data collection instruments were elaborated: a form, a manual, and procedures for data collection. Besides, as a result of the practical application of these instruments, a database - which allowed the definition of the method proposed for analysis of the causes of traffic accidents - was created. As a mean of validation of the method, an applied study and the data analysis of the observed traffic accidents are presented.
716

Análise de conforto e elastocinemática das suspensões de duplo estágio de um veículo de competição off-road em ambiente multicorpos / Elastokinematic and ride analisys of a off-road competition vehicle double rate suspension using a multibody model

André Luis Vieira Soares 06 February 2006 (has links)
Este trabalho apresenta o estudo da dinâmica vertical de um veículo off-road de competição e do comportamento elastocinemático de suas suspensões primárias de duplo estágio com o auxílio da ferramenta computacional de simulação de sistemas multicorpos MSC-ADAMS. O modelo multicorpos do veículo inclui os modelos da suspensão dianteira, suspensão traseira, sistema de direção, pneus e massa suspensa. As análises elastocinemáticas das suspensões definiram geometrias que permitem longos cursos de trabalho das suspensões sem variações indesejadas de parâmetros de projeto. Com a análise modal do modelo de veículo completo foram definidos os valores de rigidez das molas das suspensões de duplo estágio que resultaram em valores de freqüência natural no primeiro estágio semelhantes aos indicados para carros de passeio e no segundo estágio, próximos dos encontrados em veículos de competição. A análise de conforto do veículo durante simulação de passagem por trecho de pista demonstrou que os elementos de força definidos na análise modal resultam em níveis de conforto raramente encontrados em veículos de competição. / This dissertation presents the study of a off-road competition vehicle ride and the double rate suspensions elastokinematic behavior using the multibody software MSC-ADAMS. The vehicle multibody model includes the rear and front suspensions, the steering system, the tires and the sprung mass. The suspensions elastokinematic analysis defined geometric configurations that allowed long jounce and rebound travel of wheel, without undesirable project parameters variations. In the modal analysis of the vehicle multibody model, the springs rates that results in natural frequencies values similar to passenger cars for the first suspension stage and, for the second stage, similar to competition vehicles, were defined. The ride analysis during the simulation of the vehicle running on a rough track showed that the force elements defined on the modal analysis resulted in a good ride quality, rarely found in competition vehicles.
717

Método para análise de acidentes de trânsito com a identificação de fatores causais

Chagas, Denise Martins January 2015 (has links)
Esta tese tem como finalidade propor um método de coleta, tratamento e análise de dados de acidentes de trânsito para aplicação no Brasil. Este método tem como um de seus objetivos reconhecer os fatores que contribuem para a ocorrência dos acidentes, visto que identificar as causas dos acidentes é fundamental na busca por soluções para o problema da acidentalidade. No Brasil as bases de dados de acidentes de trânsito são, em geral, estruturadas a partir dos registros policiais e carecem de informações adequadas para a análise da segurança viária. O método proposto neste trabalho permite registrar acidentes de modo a contemplar: as características do acidente, as circunstâncias do momento, a identificação e as características dos veículos e pessoas envolvidas. Além disso, o método permite relacionar essas informações com os fatores que contribuíram para a ocorrência dos acidentes. Nesse contexto, a criação de uma base de dados de acidentes e seus fatores contribuintes, vem suprir a carência de informações essenciais para o diagnóstico e encaminhamento de soluções adequadas para os problemas motivadores dos acidentes de trânsito. A proposta desta tese está baseada em uma abordagem que combina aspectos qualitativos e quantitativos, alinhada às melhores práticas internacionais na área de segurança viária. Como resultado do desenvolvimento do método, foram elaborados instrumentos de coleta de dados contendo um formulário, um manual e procedimentos para a coleta de dados. Como resultado da aplicação prática desses instrumentos, foi criada a estrutura de uma base de dados que permitiu a definição do método proposto para a análise das causas de acidentes de trânsito. Como meio de validar o método proposto, foi realizado um estudo aplicado e são apresentadas as análises de dados dos acidentes de trânsito observados. / This thesis has the purpose of presenting a method for collecting and processing data on traffic accidents to be applied in Brazil. This method aims to acknowledge the contributor factors for the occurrence of accidents, since identifying the causes of accidents is crucial on the search for effective solutions for the road safety problem. Traffic accidents database in Brazil are generally structured based on police reports, therefore lacking adequate information for the analyses of road safety. The method proposes a registry of the accidents comprising accident characteristics, scene circumstances, vehicle as well as involved people identification and characteristics. Moreover, it allows relating that information with the accident contributory factors. In this scenery, the creation of an accident database and its contributory factors emerge to supply the lack of essential information for the diagnosis and adequate solution for traffic accidents. This thesis’ proposal has an approach that combines both quantitative and qualitative aspects, seeking to level up to the best international practice on the road safety area. As a result of the development of the method, data collection instruments were elaborated: a form, a manual, and procedures for data collection. Besides, as a result of the practical application of these instruments, a database - which allowed the definition of the method proposed for analysis of the causes of traffic accidents - was created. As a mean of validation of the method, an applied study and the data analysis of the observed traffic accidents are presented.
718

ROAD: REPOSITÓRIO SEMÂNTICO DE OBJETOS DE APRENDIZAGEM PARA DISPOSITIVOS MÓVEIS / ROAD: SEMANTIC REPOSITORY OF LEARNING OBJECTS FOR MOBILE DEVICES

Franciscato, Fabio Teixeira 20 April 2010 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Many Web systems are being adapted for execution and visualization in mobile devices. Learning Objects (LO) are no exception and are largely used as a pedagogic resource in the context of M-Learning. However, one of the main problems of the regular Web is also found in the mobile Web. The loss of meaning and structure related to the information prevents the realization of efficient and specific consults. In the scenario of this dissertation these limitations have prevented the recuperation of specific Learning Objects for the users educational necessities. Furthermore, when these Learning Objects are consulted through mobile devices, the limitation is maximized by the loss of standardization in these devices, either related to hardware or to software. With the objective of minimizing these restrictions, a Learning Objects repository is proposed in this dissertation - ROAD, which applies the standards of Semantic Web in order to better structure the context of the LOs by adding the intended semantic to them, specifically using the concept of Ontologies. Beyond those standards, the ROAD uses technologies that allow the identification of the mobile device being used for access so to the LO can be filtered according to the technological characteristics of the mobile device. The context of use of the ROAD will be based on two modules: ROAD as a support for the traditional classroom, which will utilize the students mobile devices available in class as a tool in the teaching/learning process; and, the ROAD as free access to the Learning Objects based on the potentialities offered by the M-Learning, which allows a utilization that does not depend on place or time and can be accessed by a user on the go. / Muitos sistemas Web estão sendo adaptados para execução e visualização em dispositivos móveis. Objetos de Aprendizagem (OA) não fogem a essa regra e são muito utilizados como recurso pedagógico no contexto da Mobile Learning. Todavia, um dos principais problemas da Web continua a existir também na Web móvel. A falta de significado e estrutura atrelada às informações prejudica a realização de consultas eficientes e específicas. No cenário desta dissertação, essa limitação prejudica a recuperação de Objetos de Aprendizagem específicos para as necessidades educacionais dos usuários. Nesse sentido, quando esses OA são consultados, através de dispositivos móveis, a limitação é potencializada pela falta de padronização tanto em hardware quanto em software desses dispositivos. Com o objetivo de suprir tais restrições, nesta dissertação, foi proposto um repositório de Objetos de Aprendizagem - o ROAD o qual aplica os padrões da Web Semântica para melhor estruturar o contexto dos OA, adicionando a semântica desejada aos mesmos, utilizando-se principalmente do conceito de Ontologias. Além desses padrões, o ROAD faz uso de tecnologias que permitem a identificação do dispositivo móvel de acesso, para assim, filtrar os OA em função das características tecnológicas de cada dispositivo móvel. O contexto de utilização do ROAD é baseado em dois módulos: o ROAD como apoio à sala de aula presencial, o qual aproveita a disponibilidade dos alunos terem dispositivos móveis em sala de aula, a fim de que os utilizem nos para um processo de ensino/aprendizagem; e, o ROAD como acesso livre aos Objetos de Aprendizagem, que baseia-se nas potencialidades que a M-Learning proporciona, ou seja, sua utilização independente de local e hora, oferecendo a possibilidade de o usuário até estar em deslocamento.
719

Problematika odborné způsobilosti řidičů motorových vozidel k provozu na pozemních komunikacích ČR / The Issue of the Competence of Drivers of Motor Vehicles to Drive on the Roads of the Czech Republic

Chodurová, Zuzana January 2014 (has links)
The theme of this master’s thesis is The Issue of the Competence of Drivers of Motor Vehicles to Drive on the Roads of the Czech Republic. It includes an analysis of the current state legislative requirements for obtaining professional qualifications of drivers, health qualification and improves their professional competence for the purposes of professional competence and analysis of selected specific road safety. In light of the findings was performed the analysis of traffic accidents in the Czech Republic. Based on the analysis of traffic accidents was the practical part of a questionnaire survey and proposals aimed at improving safety on the roads.
720

Electrical properties of road materials and subgrade soils and the use of Ground Penetrating Radar in traffic infrastructure surveys

Saarenketo, T. (Timo) 01 November 2006 (has links)
Abstract This PhD thesis is composed of a synopsis and five published papers that are focused on both the research results of studies on electrical properties of road materials and subgrade soils and their seasonal changes and the use of Ground Penetrating Radar technique in traffic infrastructure surveys. The data for this survey was collected mainly in Finland, Texas, Scotland and Sweden and thus presents many kinds of road materials, subgrade soils and climate conditions. The synopsis of this work begins with a presentation of the theory and basic principles of GPR techniques. Special attention is given to the dielectric properties and seasonal changes of unbound road materials and subgrade soils. The synopsis also presents different kinds of GPR hardware systems as well as recommendations and experiences from different data collection, processing and interpretation techniques. Special attention is given to a method whereby GPR data is integrated with other road survey data and then analysed using a number of structural diagnostic methods. Finally, the synopsis provides an overview of of the various GPR applications on roads and streets, bridges, railways and airports. The laboratory test results presented in this work show that the relationship between dielectric value and increasing water content is not linear or exponential but more likely a series of logarithmic functions. Laboratory results also showed that dielectric dispersion, which can be related to poorly performing subgrade soils and road aggregates, takes place mainly in loosely bound adsorption water and capillary water layer. As such these moisture sensitive problem materials can also be identified during the dry summer seasons when they are stiff. Dielectric value and electrical conductivity can also be related to other technical properties of road materials and subgrade soils such as frost susceptibility, shear strength, plastic limit, compaction degree and voids content. Laboratory tests and field data collected using the Percostation technique also demonstrate that a knowledge of seasonal changes and thermodynamics is very important in understanding and modelling the mechanical behaviour of road structures. Finally, laboratory and field tests indicate that colloids have an important role in the failure mechanism of the road materials. This research demonstrates that the GPR technique not only gives valuable structural information on the different types of structures and subgrade soils but it provides a wide range of information of the electrical properties of the materials under survey which can be further related to their mechanical performance. The best information will be gained if GPR data is analysed together with other non destructive testing data collected form the roads, railways and airports.

Page generated in 0.12 seconds