Sharif Digital Repository

Pricing users of the network in the congested Central Business District (CBD) will cause change in the travel behavior of the different sectors of these users . The problem of optimal pricing of CBD is formulated in this study as a bilevel optimization . The lower level problem is a joint trip production-distribution-mode choice-assignment problem , which identifies three groups of the users , namely shoppers , retailers and basic employees . The upper level problem maximizes total long-run benefit and minimizes air pollution and changes in attractions of the zones . The demand for shoppers and retailers is elastic , but that of the basic employees is assumed inelastic . The decision... 

Pavement maintenance and rehabilitation is an important problem in road pavement programming. Pavements experience significant distress over its life due to passage of vehicle (particularly heavy trucks), as well as abrupt variation in temperature (freeze and thaw). This would deteriorate pavements and reduces their serviceability. Rise of pavement maintenance costs places higher importance upon the need for maintenance programming. This study employs an evolutionary model to optimize the long-run benefit of the maintenance program. The model is stochastic in nature, and imbeds a Markovian decision procedure in the model to take into account such variabilities. The model is applied on... 

Transportation networks are considered as complex systems, and in many cases they behave in such an irregular and unexpected manner. Such complexities cause problems in studying the behavior of these systems. An example of such complexities is chaos in the network flows. On the other hand, the behavior of these networks is highly affected by the incidents like accidents and bad weather. Such events affect the level of service and travel time reliability of the networks. In this research, a dynamical approach to traffic assignment has been chosen to model chaos and uncertainties in the network. By using this approach for modeling flow evolution, edge of chaos and uncertainty in supply and... 

Two significant features of a transportation network, uncertainty and complexity, might cause some irregular behaviors. One example of such behaviors is chaotic flow in which the transportation system fails to reach equilibrium and people experience different daily travel times. These uncertainties are not controllable in any transportation system and, if not taken into consideration, will result to low levels of service and poor reliability. In this study, an evolutionary traffic assignmet model is used to illustrate when the network reaches bifurcation and chaos. Later, the effects of uncertainty in the parameters of supply and demand is tested on the evolutionary traffic assignment model.... 

One effective way to reduce air pollution created by automobiles is to tax/toll the unfavorable characteristics of the automobiles. This study is an extension of the current literature on taxing visible and measurable aspects of automobile ownership and use, namely engine size, age, fuel used, and technology level. A three sided model, comprising the operator (government), consumers, and automobile producers, has been constructed to control emission by proper taxation. Engine size tax is one-time, age-tax is yearly, and fuel use is usage-based. The model has been built and experimented based on a sample population and the results have been shown to be in the direction of the management... 

There is a two-way relationship between land use and transportation. So each of them can be used to manage and control the other one. Land use can be Auto-Oriented, or Transit-Oriented. Auto-Oriented Development leads to urban sprawl, causing longer trips and increasing use of private cars. Problems related to this type of development appeared by the end of the 20th century. On the other hand, Transit-Oriented Development may lead to higher density areas, and higher transit use, providing better space for pedestrians and cyclists, as well as increasing environmental pollutions. Land use-transportation relationship hs been the subject of many recent studies. One of the previous models... 

Natural disasters have been with the earth, and felt critical as far back as human history. These incidents are inevitable, but their effects may be controlled. One important problem after a disastrous earthquake is the management of people’s vehicular movements in a chaotic situation. This study is an endeavor to envisage what would possibly happen after such an incident, and how could we possibly control or manage the traffic in such an occasion. We start with the analysis of the online reports of similar past incidents, and try to picture how people react to these events. We try to identify the trip purposes that have been shown to be pursued, and the respective origins and destinations.... 

Transportation systems are dynamic and complex systems due to the interaction between human and non-human factors. In certain circumstances, the dynamics of traffic flow causes the transportation system fail to reach equilibrium and chaos will occur. In such cases, travel times vary daily and travel time reliability decreases. Moreover, these systems are continuously exposed to incidents that cause a high degree of uncertainty. So, it is necessary to enter such dynamics and uncertainty in the decision making models, such as network design. In this study a bilevel network design problem is defined with chaos and uncertainty taken into account. At the higher level problem, the optimization... 

One of the main challenges construction industry face is the shortage of skilled labor. It is also one of the main reason of project’s delay. Many strategies including compensation payment, longer hiring duration and increase in wages has been proposed. Conventional scheduling assumes unlimited amount of resources or if consider the resource, is restricted to single-skilled resource. This is in contrast with real-world where workers may not be available at any time or they may possess a range of skills. Multiskilling is a workforce strategy that has been shown to reduce indirect labor cost, improve productivity and make the planning more realistic. Past researches proposed algorithms using... 

Tehran is one of the most polluted megacities in the world, and based on different studies, vehicular sources are responsible for most of the criteria pollutant emissions in this city. The number of vehicles on the streets has been increased drastically leading to growing amount of emission and this trend is continuing. In order to reduce the amount of vehicular emission, it is vital to investigate the factors affecting vehicles emission in this city. This could help to find efficient solutions to improve the situation. Hence, a low-cost methodology to estimate the vehicular emissions is developed. In this... 

In this research, the effect of uncertainty on the Logit and probit discrete choice models’ results during a route choice situation is assessed. Researchers measure average travel time or calculate it with traffic assignment modules. However, just like any other random variable, the estimated or measured average travel time does not have a certain value and has measurement errors. Logit and Probit models are the most commonly used discrete choice models yet none of them are capable of considering the independent variable’s uncertainty. The amount of difference between models overlooking independent variables’ value uncertainty and the variation of the model capable of considering these... 

Estimation of demand, for example, for transportation is an important issue for the planning and programming of various systems. Thus, enhancing the predictability power of such models is of high value. Demand stems from choices of individuals, and choice is subject to uncertainty and fuzziness. Uncertainty comes from many factors including incomplete information of decision-maker, and fuzziness comes from many other factors including personal perception regarding the value of the variables affecting choice. This study tries to introduce a new approach in building choice models, in which variables are transformed into another variable by the help of a global wisdom. This wisdom shows the... 

One important problem in all, particularly in developing countries, is shortage of funds to invest in infrastructure projects. One way to lessen this difficulty is to benefit from the private sector participation in this respect. Build-Operate-Own-Transfer (BOT) is a Public-Private-Partnership (PPP), in which the private sector invests and builds a (e.g. road) project, operates it for a specified period of time to collect the tolls to return the investment cost plus the specified attractive rate on it, and then transfer it to the public sector. This research, which is a continuation of previous endeavors in this area, formulates the problem, discusses the multiplicity of the solutions, and... 

Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's...