Sharif Digital Repository

Crash data availability is a significant requirement for identifying hazardous roads. However, for roads with poor data sets or no crash record, a method is needed to find and rank road segments independent of the crash records. In this paper, an auditing based methodology is proposed to determine the hazardous locations. A Rural road is investigated by decomposing it first into six elements, and then into safety factors corresponding to each element. The elements are: straight segments, horizontal and vertical curves, bridges, tunnels, merges and intersections, and side road land use. The relative contribution of the elements to the safety of a road segment is determined using the... 

Many research works in mathematical modeling of the facility location problem have been carried out in discrete and continuous optimization area to obtain the optimum number of required facilities along with the relevant allocation processes. This paper proposes a new multi-objective facility-location problem within the batch arrival queuing framework. Three objective functions are considered: (I) minimizing the weighted sum of the waiting and the traveling times, (II) minimizing the maximum idle time pertinent to each facility, and (III) minimizing the total cost associated with the opened facilities. In this way, the best combination of the facilities is determined in the sense of... 

In this paper, we propose an optimization framework to retrieve an optimal group of experts to perform a given multi-aspect task/project. Each task needs a diverse set of skills and the group of assigned experts should be able to collectively cover all required aspects of the task. We consider three types of multiaspect team formation problems and propose a unified framework to solve these problems accurately and efficiently. Our proposed framework is based on Facility Location Analysis (FLA) which is a well known branch of the Operation Research (OR). Our experiments on a real dataset show significant improvement in comparison with the state-of-the art approaches for the team formation... 

Frequency estimation of vapor cloud explosions (VCE) are traditionally based on sparse VCE incidents data analysis while process conditions that generate VCE's have a wide spectrum giving VCE's with different strengths. The present paper is focused on developing a systematic methodology to estimate the frequency of VCEs based on process and plant conditions in order to find optimal location of a control room using quantitative risk assessment (QRA). In the presented approach, after classification of plant areas according to variables likely to generate different release conditions, a comprehensive release study is carried out to determine individual probable leakages. Consequently, only... 

In this study, we consider a capacitated location–multi-allocation–routing problem with population-dependent random travel times. The objective is to find appropriate locations as server locations among the candidate locations, allocate the existing population in each demand node to server locations, and determine the movement path of each member to reach its corresponding server with respect to the simultaneous change of the random travel times so that the expected total transportation time is minimized. In our study, the concept of population-dependent random travel times incurs two issues: (1) consideration of some random factors in computing the travel times and (2) impact of the... 

In this study, the optimal location of baffle in the header of air-to-air plate heat exchangers and the geometry of the header and the effects of triangular fins arrays on the effectiveness were numerically investigated for different flow rates and Reynolds numbers on different models. The main purpose of inlet baffle and geometry changes is to improve the pattern of flow distribution and assist flow uniformity. The investigations show that the optimal location of the inlet baffle with high Reynolds numbers has an insignificant effect on effectiveness, while with Reynolds numbers 250-3000, the effectiveness is affected significantly by baffle location. On the other hand, the reduction in... 

This Paper presents a model for optimal locating and sizing of Distributed Generation (DG) for congestion management in deregulated electricity market. For reducing the solution space a priority list of candidate buses is formed and then optimal placement and sizing of DG in potential buses is discussed. In order to incorporate stochastic nature of power system in this study, Monte-Carlo method is used to simulate the effect of uncertainty of loads and system on the optimal location and size of the DGs in the network. The proposed method is applied to IEEE Reliability Test System (RTS). The impacts of load uncertainty on optimum DG size and location are studied  

This article studies the problem of locating fuel stations to minimize the extra cost spent in refueling detours, which belongs to a class of discretionary service facility location problems. Unlike many studies of similar problems in the literature, the proposed model considers capacity constraints and compares different ways to incorporate them in the formulation. Note that ignoring the capacity constraint results in nonoptimal and unrealistic solutions. The proposed models are solved using both an off-the-shelf solver (CPLEX) and a specialized meta-heuristic method (Simulated Annealing) developed in this study. The solution methods are tested and compared in two case studies; a test... 

This paper models a novel and practical bi-objective hub-location problem under a centralized carrier collaboration framework between one holding company and multiple carriers. The holding company first establishes a hub-and-spoke network in order to locate p hubs and to assign the center nodes to the located hubs. Then, it allocates the transportation routes of the hub network to the carriers. In contrast, the carriers should select an appropriate vehicle type to serve the transportation requests in a green hub network. The carriers are also able to meet the transportation requests within a certain time-window based on a soft time-window mechanism. Moreover, aiming to emphasize green... 

Fixtures play a key role in locating workpieces to manufacture high quality products within many processes of the product lifecycle. Inaccuracies in workpiece location lead to errors in position and orientation of machined features on the workpiece, and strongly affect the assemblability and the final quality of the product. The accurate positioning of workpiece on a fixture is influenced by rigid body displacements and rotations of the workpiece. In this paper, a systematic approach is introduced to investigate the located workpiece position errors. A new mathematical formulation of fixture locators modeling is proposed to establish the relationship between the workpiece position error and... 

Sectionalizing switches (SSs) are often presumed to function fully reliable. However, SSs are exposed to have some malfunctions, whereby undermining their ability to improve service reliability. This study presents a model to integrate SS malfunction probability into SS placement problem. The model aims to minimize the total SSs costs as well as customers interruption cost. The proposed model is formulated in mixed integer programing (MIP), which can be easily solved via several available solvers and gain global optimal solution. The proposed model indicates the extent to which the placement problem is affected by uncertainty associated with SSs functionality, and how not considering SSs... 

For a set of colored points, a region is called color-spanning if it contains at least one point of each color. In this paper, we first consider the problem of maintaining the smallest color-spanning interval for a set of n points with k colors on the real line, such that the insertion and deletion of an arbitrary point takes O(log2 n) the worst-case time. Then, we exploit the data structure to show that there is O(n log2 n) time algorithm to compute the smallest color-spanning square for a set of n points with k colors in the plane. This is a new way to improve O(nk log n) time algorithm presented by Abellanas et al. [1] when k = !(log n). We also consider the problem of computing the... 

A bi-objective stochastic capacitated multi-facility location–allocation problem is presented where the customer demands have Bernoulli distributions. The capacity of a facility for accepting customers is limited so that if the number of allocated customers to the facility is more than its capacity, a shortage will occur. The problem is formulated as a bi-objective mathematical programming model. The first objective is to find optimal locations of facilities among potential locations and optimal allocations of stochastic customers to the facilities so that the total sum of fixed costs of establishment of the facilities and the expected values of servicing and shortage costs is minimized. The... 

Today, communication science is advancing very rapidly; one of these advances is mobile location determination which means finding position of a mobile station. There are some methods to location determination; one of these methods is Signal Strength (Power of Arrivals). In this research, Mobile Location Determination using enhanced signature database method in a Location grid will be introduced; several ways for positioning error reduction will also be described. © 2009 IEEE  

In this study, the authors propose an algorithm to reduce the effect of antenna location uncertainty for locating moving targets in multiple-input multiple-output (MIMO) radar systems. The proposed method is a closed-form solution which employs the measurements of multiple independent targets to alleviate the antenna location uncertainties. The authors establish a pseudo-linear set of equations by using the range and the range-rate auxiliary parameters, which allows the problem to be solved using a two-stage weighted least squares estimator. The proposed method is shown analytically and confirmed by simulations to attain the Cramer-Rao lower bound under small error conditions. The... 

A bi-objective stochastic capacitated multi-facility location–allocation problem is presented where the customer demands have Bernoulli distributions. The capacity of a facility for accepting customers is limited so that if the number of allocated customers to the facility is more than its capacity, a shortage will occur. The problem is formulated as a bi-objective mathematical programming model. The first objective is to find optimal locations of facilities among potential locations and optimal allocations of stochastic customers to the facilities so that the total sum of fixed costs of establishment of the facilities and the expected values of servicing and shortage costs is minimized. The... 

Geothermal energy is a type of renewable energy with high availability and independence from climatic and atmospheric conditions. It has been shown that geothermal energy is technically, economically and environmentally more suitable for hydrogen production than other renewable sources. Hydrogen has wide applications in many fields including cooling, oil, gas, petrochemical, nuclear, and energy industries. Afghanistan has significant potential in geothermal power generation and also several hydrogen-consuming industries that provide opportunities for geothermal-based hydrogen production. This study attempted to find suitable locations for the construction of geothermal power plant for...