Sharif Digital Repository

Ant algorithms are optimization algorithms inspired by natural behavior of real ants, which can find the shortest path between nest and food. These algorithms are used to solve numerous complex optimization and combinatorial problems. In recent years, ant algorithms have been used in image processing, specially in edge detection. Edge detection being important and having applications in image processing, several edge detection algorithms have been presented. Our goal is to study edge detection processes based on ant algorithms. Four algorithms recently proposed in the literature are implemented, and the results presented by their authors are verified. Furthermore, implemented algorithms are... 

Increasing population and rapid industrial development has resulted in increasing energy consumption exponentially. Limited resources of fossil fuels have forced industrialized countries to reduce energy consumption by modern systems as much as possible.
Poultry farms consume about 1,400 million liters of gas oil per year and 38% of total consumption in the agricultural section; then they are the largest consumer of this industry in Iran. Unfortunately traditional heating systems and poor control of indoor conditions are some of the most important factors affecting energy consumption in poultry farms. With the air ventilation rate of a salon equal to the amount of air needed for birds up... 

In general, reliability is the ability of a system to perform and maintain its functions in routine circumstances, as well as hostile or unexpected circumstances. Redundancy Allocation Problem (RAP) is a combinatorial problem where it is going to maximize system reliability by discrete selection from available components. The main purpose of this study is to prove the effectiveness of robust optimization to solve RAP. Generally, robust optimization is a field of optimization theory where robustness is sought against uncertainty and/or variability of parameters' values. In this study it is assumed to have Erlang distribution density for components' failures where to implement robust... 

Feeder reconfiguration is one of the most prominent tasks for loss reduction, reliability improvement and also congestion alleviation in distribution networks. Besides improving abovementioned operational issues, during a long period of time, proper switching in appropriate times can causes a lot of economic savings. Furthermore, it can be intensified when capacitors are implemented and controlled in the network. To reach this purpose, most of the previous literature focuses merely on the power grid reconfiguration. Few of these researches have considered this problem as a dynamic one and studied that in a period of time, e.g. one day, considering fixed level of loads despite the others that... 

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.... 

Protecting sensitive data stored in database systems, especially in outsourced ones, has become a major concern in many organizations. One of the main possible solutions is to encrypt data before storing them on databases. Bucket-based encryption is among different approaches proposed to accomplish this goal which besides its various benefits, suffers from generating false-positive results. Multi-join queries are one of the most important operations in database systems and their usage grows rapidly in comparison to other types of queries by increasing the size of stored information. While using the decision support systems and data mining solutions are growing continuously, executing... 

Given the increased competition in supply chains and enlargement of their scale along with increasingly significant role of distribution systems, design and optimization of novel systems with comprehensive approaches in a timely manner has become important more than ever. One of such modern, efficient systems is cross docking in which the distribution network is omitted and thus operations are carried out faster and the productivity is increased. In this system, processes like packaging is done in cross docking and the goods and products are directly sent to customers. This study investigates a long-term and a short-term approach to the design of in two distinct problems. In the first... 

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... 

Process plants such as refineries and petrochemical plants are complex facilities consisting of equipment, piping systems, instruments, electrical systems, computers, and control systems. Process units design is mostly based on designer`s experience and design general criteria and standards. Using mathematical methods to optimize the design may have an effective role in cost reduction and it would give the designer some general view in case that the exact design is not applicable.
Optimization of Process units is described in this study. This optimization includes the exact location of each equipment, nozzle, pipe rack and also pipe route layouts. Mixed integer linear programming (MILP)... 

Graceful and α-valuation are the first labeling methods which was introduce in the late 1960. α-Vaulation of a graph is a special cases of graceful labeling. Despite of the large number of papers published on this subject, in literature, there are few particular techniques to find labeling of graphs. There are still many open problems on this subject ,some of which are well-known in graph theory. In this research, a new mathematical integer model and two constraint programming models are presented for the graph valuation problem in the case of quadratic graphs. Then, a comparision between their results are discussed. The advantages of this model is linearity, independence from graph... 

When the reservoir energy is too low for the well to flow, or the production rate desired is greater than the reservoir energy can deliver, it becomes necessary to put the well on some form of artificial lift to provide the energy to bring the fluid to the surface. Continuous flow gas lift is one of the most common artificial lift methods widely used in the oil industry. In continuous gas lift, gas at high-pressure is injected in a suitable depth into the tubing, to gasify the oil column, and thus facilitate the production. Every well has an optimal gas lift operating point at which it will produce the most fluid. Ideally, if there is no restriction in the total amount of gas available,... 

Wireless sensor networks have been widely used in such areas as intelligent transport systems, military systems and etc. Wireless sensor networks are composed of a number of sensor nodes in charge of data collection, analysis and transport. The energy limitations on wireless sensors have brought researchers to work on algorithms intended for efficient use of energy and therefor maximum network life.
In this work, we will first present a detailed description of two well-known protocols: LEACH and AODV. In the second part, an optimized routing protocol for wireless networks, based on the previously described protocols and the ant colony theory will be presented. The optimized protocol will... 

Environmental problems and the consequent governmental regulations, has led supply chains into reverse and closed-loop supply chains. Application of problems such as "Vehicle Routing Problem” has diminished in the closed-loop supply chain, and instead of them, the problem of "Vehicle Routing Problem with Deliveries and Pickups" has become more important. On the other hand, tendency of supply chains to running information in the chain in a desired way, has led to grow the attention to establishing policies of “Vendor Managed Inventory". It seems that by tending the supply chains to closed-loop supply chains which are utilizing the policy of "Vendor Managed Inventory", application of problems... 

Throughout history, natural and unnatural disasters have caused great financial and human losses to human beings. Although these incidents are sometimes unpredictable and inevitable, with proper management, the casualties can be reduced. To optimally manage disaster response operations, it is essential to understand people’s vehicular movements in chaotic situations. This can be achieved by examining previous earthquakes. In the post-earthquake conditions, as the network experiences sudden and heavy loading, not only the debris falling on the roads but also the traffic congestion caused by the scared people will cause the links to close, and this will disrupt the relief and rescue...