Sharif Digital Repository

Search engines have an important role in providing the appropriate response to the user’s search. In the past, all people had received the same result for searching an equal expression. Now, no one receives a similar answer by searching in Google or Bing. The information in the net is getting bigger day by day. Thus, websites owners face a serious challenge to provide a suitable and relevant information for the users. Accordingly, ranking the results for users is difficult. To address this issue, researchers proposed different ranking algorithms for sorting the search results. Travel and tourism is one of the most competitive and cost-consuming in the field of electronic commerce especially... 

In this thesis, a special case of the Traveling Purchaser Problem (TPP) is considered in which instead of one vehicle there are multiple vehicles as purchasers. Furthermore, the vehicles start their path from a set of starting points and after visiting a number of markets they return to the depot. Moreover, each of the products needs a special loading condition and the vehicles have multiple compartments to meet these loading constraints and the products are loaded in their appropriate compartments. This problem is at first modeled as a MIP formulation and then by decomposing the problem a Column Generation procedure is developed to solve the problem. To enhance the speed of the column... 

The human need for reliable and accessible energy sources for household, industrial, transportation, etc. caused the discovery of the first oil well to move towards exploitation and use of this large, cheap and available energy source, accelerated. With the start of this movement, oil and its products in the last two centuries have quickly established themselves as a major part of the energy basket of most countries in the world. The entry of crude oil and its products into the energy industry has faced new issues and challenges for decision makers in this field. One of the most important challenges has been the planning and management of the process of distribution and transfer of petroleum... 

In this study, providing home care services by hospitals in the epidemic situations such as COVID-19 is proposed for the first time. Moreover, a mathematical formulation is developed to provide simultaneous decision-making about serving patients without COVID-19, scheduling nurses in the non-COVID-19 wards of hospitals, and scheduling and routing for nurses to serve patients at home. This problem aims to develop essential compatibilities to keep people safe and help continue vital healthcare services during the COVID-19 and similar pandemics. Accordingly, nurses' preferences, the number of available hospital beds, the patient-to-nurse ratio, the Unavailability of some nurses due to COVID-19,... 

Examples from recent years, such as Covid-19 disease and earthquakes, show that disasters can have devastating effects on a community.These disasters are divided into two categories: expected and unexpected. decision makers cannot easily determine the time, severity and effects of them. Therefore, they must coordinate their decisions in the pre-disaster and post-disaster stages according to the incomplete information available, and according to the dynamics of the situation, quickly understand and interpret the connections between different decisions. Among the various approaches, the decision support system can explore the variable and unpredictable nature of such issues and enable decision... 

This study offers a framework to manage mass vaccination programs in response to an outbreak in a city. Compared to previous studies, we consider more operational challenges in the vaccination process; for example, transshipment between vaccinations units and availability of second doses. Our objective function is based on the risk of unvaccinated individuals. Therefore, the model aims at favoring those places in the city where the risk of unvaccinated people is high. Using different kinds of vaccines is another factor that our mathematical model includes. Vaccines are categorized into single-dose and double-dose classes. In this regard, the balanced access to different vaccine types is of... 

Peoples need financial resources to improve their quality of life, and companies need them to progress and increase their comparative advantage. Borrowing is one of the most popular methods of financing. Peer-to-peer lending, also known as "marketplace" or "social" lending, is a novel form of intermediation that expunges the role of financial institutions (like banks) as an intermediary and allows entities (individuals or businesses) to raise loans directly from other entities. This lending platform can provide better quality services to borrowers (by quickly providing a simple loan application process through a transparent and flexible portal) and lenders (by managing their funding and live... 

Procurement field and supplier’s selection are key decisions in the supply chain in today's business environment.In this problem, both procurement and transportation costs are important. The Traveling Purchasing Problem (TPP) belongs to this field of study. In spite of many researches in the TPP, most of the researches are confined to one single purchaser. In this research, a new variant of Traveling Purchaser Problem is proposed with priority in purchasing. The priority policy is assumed for every single of products and the purchasers’ objective is to meet all of the demands according to their priority and vehicle's capacity in the lowest cost. In this regard, the purchaser has to buy the... 

Breast cancer has been one of the main causes of women's deaths in recent years. Today, various methods are used to treat this disease, among which intensity-modulated radiation therapy is one of the most common methods. The goal of radiation therapy is to destroy cancer cells while protecting the surrounding healthy tissues. In left breast cancer, due to the proximity of the heart and breast tissue, we are at risk of delivering an excessive dose to the heart and increasing cardiac complications after the treatment. In addition, due to the irregular and unpredictable breathing movements of the patient during the treatment and the resulting uncertainty, we face more challenges. In order to... 

Parallel machine scheduling problems are the decision-making process of allocating limited resources to activities over time. These issues have attracted a lot of attention in the past decades based on their applications in the real world. It can be discussed about the application of parallel machine scheduling problems in computer processing, production lines and multi-stage systems as examples of areas where parallel machine is observed. Most of the research on parallel machine scheduling has focused on the optimization of a single criterion such as total or average task completion time, total completion time with different weights, sum of penalty or tardiness penalty, total number of... 

Research and information available shows that the number of natural disasters are increasing dramatically; hence disaster management is being raised as one of the most important topics in this field. The relief logistics is the greater part of disaster management model.
In this study, in order to manage the logistics activities effectively in a response phase of an earthquake, a hybrid meta-heuristic algorithm is developed for a transportation network. Then, the proposed algorithm is tested on a small part of Tehran.
 

In recent years, simulation optimization methods have been developed to solve complicated problems that cannot be solved by mathematical programming methods. In simulation optimization methods, first the problem is modeled by simulation tools and then by applying optimization tools the optimal combination of input variables that optimizes the simulation output is determined. Although simulation optimization has attracted researchers’ attention in recent years, most of the works presented do not consider uncertainty in simulation models. This becomes our motivation in this study to develop uncertain methods in metamodel-based simulation optimization based on minimax methods that are... 

Patient scheduling is one of the most important problems in healthcare optimization which has been in center of attention in various environments including outpatient clinics and operating rooms. Effective scheduling systems have the goal of matching the demand with capacity so that resources are better utilized and patient waiting times are minimized. Furthermore, patient scheduling can be merged with another problem in which the main goal is to find the optimal sequence of a given list of patients. Moreover, there are several sources of uncertainty such as patients’ unpunctuality, absence, and service time in this problem resulting in having a very complex problem. In this research,... 

Outpatient clinics always encounter a huge deal of demand and due to the variety of the services they provide and the existence of uncertainties, operation management is such a difficult task. This issue has made problems related to this issue popular among scientists and researchers. In this research, we are going to address several popular problems related to outpatient appointment scheduling. Initially, an M/M/c/K queuing system is developed in order to obtain the optimum scheduling window for different sub clinics. Secondly, the real demand for each sub clinics will be estimated using data analysis techniques for each 24-hour period. Having the results of the previous section, we build a... 

The Multi-Depot Traveling Purchaser Problem under Shared Resources (MDTPPSR) is a new variant of the Traveling Purchaser Problem (TPP). In this problem, each depot can purchase its products using the shared resources of other depots, and vehicles do not have to return to their starting depots. The routing of this problem is a Multi-Trip, Open Vehicle Routing Problem. A tailored integer programming model is formulated to minimize the total purchasers’ costs. Considering the complexity of the model, we have presented a decomposition-based algorithm that breaks down the problem into two phases. In the first phase, tactical decisions regarding supplier selection and the type of collaboration are... 

In this thesis, the Conditional Value-at-Risk measure (CVaR) is used in two basic decision making problems under uncertainty. This measure is used previously in the field of risk management. The first problem is decision tree problem which is a multi-stage stochastic decision problem. In this problem, the risk of a decision maker is estimated by CVaR measure and a linear programming model is presented by using disjunctive programming theory. The importance of the developed model is in its generality for modeling all problems with decision tree structure. Then, its computational performance is compared to intuitive nonlinear programming models for the problem. Moreover, the presented model... 

Cloud Manufacturing (CMfg) is a service-oriented manufacturing (SOM) paradigm that provides a dynamic, scalable, and virtualized working ecosystem. The CMfg collaborative structure can be modeled as a hyper-network-based service-demand matching architecture. It is enriched with quality of service (QoS) characteristics to produce customized products in a stable and reliable network. This stability should be considered in the overall manufacturing network mechanism. This Thesis has developed a multi-dimentional model and improved it by providing absorptive and adaptive strategies utilizing available resources and capacities to enhance the system’s stability and reliability against the...