Solving routing problems using math heuristics and decomposition methods

Iris Forma-  Ph.D. student

Abstract:

Studies in the field of transportation are expanding due to the growing need of reducing costs and emission of pollution. The development of new modes of transportation in cities and the development of new ways of distribution in the supply chain present new challenging routing problems in the field of operations research. In this talk we present solution methods for two emerging routing problems: a production and distribution problem in supply chains and a repositioning problem in bike sharing systems.

Supply chain management (SCM) involves making decisions on production scheduling, inventory levels of raw materials and finished products, transportation and related aspects, with the objective of minimizing the total cost associated with these activities. While in the past, policies of different functions of the supply chain were managed separately, more recent management practice and studies recognize the advantages of coordinated decision making. We formulate the problem as a Mixed Integer Linear Program (MILP) which integrates decisions of production, inventory, and distribution of products and pick-up of raw materials. We propose and analyze three decomposition methods for solving this problem.

Bike-sharing systems allow people to rent a bicycle at one of many automatic rental stations scattered in the city, use them for a short journey and return them at any station in the city. A crucial factor for the success of a bike sharing system is its ability to meet the fluctuating demand for bicycles at each station. Thus, operators of bike sharing systems are responsible to regularly remove bicycles from some stations and transfer them to other stations, using a dedicated fleet of light trucks. We refer to this activity as repositioning bicycles and formulate it as a MILP for the case of the Static repositioning, i.e., during the night when demand is negligible. Then, we propose a three step math heuristic for solving larger networks than those that can be solved by the MILP formulation.    

This work was performed under the supervision of Prof. Michal Tzur and Dr. Tal Raviv.

ההרצאה תתקיים ביום חמישי 1.1.15, בשעה 12:00 בחדר 206, בנין וולפסון הנדסה, הפקולטה להנדסה, אוניברסיטת תל-אביב.

Daphne Weihs

Faculty of Biomedical Engineering, Technion-IIT

Traction force microscopy: what cell-gel mechanical interactions can tell us

Traction force microscopy (TFM) is a method that has been utilized in the last decade to evaluate the forces applied by cells to underlying gels. Cells utilize traction forces to adhere, move, and apply force to their environment, as part of their normal function. Variation in forces between different cell types, following treatment, or following onset of disease and can reveal dynamic structural changes within the cell that may relate to changes in cell function. The mechanical interaction of cells with their environment depends on the cell type, its current activity, and the dimensionality and stiffness of the gel. Using 2-dimensional (2D), elastic polyacrylamide gels, with fluorescent particles embedded under their surface, or 3D collagen gels with dispersed particles, we are able to quantitatively evaluate forces applied by cells. In the current talk, I will explain the TFM method and approach in 2D and in 3D gel systems, providing detailed examples from three different cell types. I will provide examples on (1) invasive cancer cells (in 2D and 3D), showing differences between cancer and benign cells (2) changes in cell-gel interactions when undifferentiated stem cells grow into a 3D embryoid body; and (3) differences between pre-adipose cells and differentiated adipocytes. The experiments highlight quantitative similarities and differences relating to cell function and activity.

ההרצאה תתקיים ביום ראשון ה 04.01.15 בשעה 14:15

בחדר 315 ,הבניין הרב תחומי ,אוניברסיטת תל אביב

Daphne Weihs

Faculty of Biomedical Engineering, Technion-IIT

Traction force microscopy: what cell-gel mechanical interactions can tell us

Traction force microscopy (TFM) is a method that has been utilized in the last decade to evaluate the forces applied by cells to underlying gels. Cells utilize traction forces to adhere, move, and apply force to their environment, as part of their normal function. Variation in forces between different cell types, following treatment, or following onset of disease and can reveal dynamic structural changes within the cell that may relate to changes in cell function. The mechanical interaction of cells with their environment depends on the cell type, its current activity, and the dimensionality and stiffness of the gel. Using 2-dimensional (2D), elastic polyacrylamide gels, with fluorescent particles embedded under their surface, or 3D collagen gels with dispersed particles, we are able to quantitatively evaluate forces applied by cells. In the current talk, I will explain the TFM method and approach in 2D and in 3D gel systems, providing detailed examples from three different cell types. I will provide examples on (1) invasive cancer cells (in 2D and 3D), showing differences between cancer and benign cells (2) changes in cell-gel interactions when undifferentiated stem cells grow into a 3D embryoid body; and (3) differences between pre-adipose cells and differentiated adipocytes. The experiments highlight quantitative similarities and differences relating to cell function and activity.

ההרצאה תתקיים ביום ראשון ה 04.01.15 בשעה 14:15

בחדר 315 ,הבניין הרב תחומי ,אוניברסיטת תל אביב