Sharif Digital Repository

This paper introduces the energy-constrained multi-visit traveling salesman problem with multiple drones considering non-customer rendezvous locations (EM-TSPDs). A ground vehicle equipped with multiple drones that can serve multiple customers per trip performs deliveries. Before solving the EM-TSPDs, the non-customer rendezvous location subproblem (NRLP) is addressed to locate candidate non-customer rendezvous nodes so that all drone customers can be covered by drones. The importance of this full coverage is that all drone customers can reap the benefits of drone delivery by receiving fast delivery or being served in areas that are inaccessible by road network. We propose MILP formulations... 

While research into various dimensions of language learning strategies has been thriving over the recent years, grammar learning strategies (GLS) have largely remained under-explored. The present mixed methods research aimed to explore GLS in the three stages of classroom grammar tasks, while striving to determine the sequence of GLS and their contribution to grammar proficiency. In the qualitative phase, 13 participants partook in stimulated recall and semi-structured interviews after completing consciousness-raising (CR) tasks. Then, the grounded theory (GT) methodology was applied to conceptualize a theoretical model. For the quantitative phase, a modified version of Pawlak’s Grammar... 

Improving the service quality of public transport is necessary to maintain the loyalty of current users and attract new travelers. Past studies show that users’ preferences for transit service quality are heterogeneous, but recognizing the factors describing this heterogeneity has not been investigated in depth. This paper aims to evaluate the sources of heterogeneity in passengers’ preferences for service attributes of bus transit regarding the regular bus system in the city of Tehran. Four attributes of bus travel, including in-vehicle travel time, fare, vehicle crowding, and headway, were considered. Stated preference (SP) data of 360 commuters with work purpose was collected through... 

This paper analyzes the oligopolistic equilibria of multiple price-maker agents in performance-based regulation (PBR) markets. In these markets, there are price-maker agents representing some frequency regulation (FR) providers and a number of independent price-taker FR providers. A model of equilibrium problem with equilibrium constraints (EPECs) is employed in this paper to study the equilibria of a PBR market in the presence of price-maker agents and price-taker FR providers. Due to the incorporation of the FR providers' dynamics, the proposed model is reformulated as a mixed-integer linear programming (MILP) problem over innovative mathematical techniques. An optimal equilibrium point is... 

In this survey, the reactive mass transfer data are determined for extraction technique in the modified rotating disc column. Mathematical models are investigated to compute the mass transfer coefficients of the dispersed phase. An increase in the dispersed phase holdup from 0.85 to 0.12 and a decrease in droplet diameter from 2.24 to 0.74 mm are observed with increasing rotation speed from 170 to 410 rpm in the optimized system. The experiments showed that the optimum transport efficiency in rotor speed of 410 rpm in this column is equal to 98.85% and 99.45% for extraction and stripping stages, respectively. The model's achievement is compared with the solvent extraction data and a... 

Reliability is an essential factor in distribution networkt expansion planning. However, standard distribution reliability assessment techniques rely on quantifying the impact of a pre-specified set of events on service continuity through the simulation of component outages, one at a time. Due to such a simulation-based nature, the incorporation of reliability into distribution network expansion planning has customarily required the application of heuristic and metaheuristic approaches. Recently, alternative mixed-integer linear programming (MILP) models have been proposed for distribution network expansion planning considering reliability. Nonetheless, such models suffer from either low... 

The application of mathematical and systematic models and approaches to health is on the rise. In this study, a mixed-integer linear programming problem with cost (staff payroll) objective function is proposed to determine homogeneous personnel shift scheduling so that the constraints of the number of personnel per shift are met. The purpose of this study is to optimize the scheduling of personnel with the same skills to minimize variable hospital costs. In a hospital, homogeneous personnel might be skilled nurses who can work in the same departments or service staff of the departments. First, a mathematical model is proposed for scheduling as a linear problem and solved using Lingo... 

The concept of flexibility is defined as the power systems’ ability to effectively respond to changes in power generation and demand profiles to maintain the supply–demand balance. However, the inherent flexibility margins required for successful operation have been recently challenged by the unprecedented arrival of uncertainties, driven by constantly changing demand, failure of conventional units, and the intermittent outputs of renewable energy sources (RES). Tackling these challenges, energy storage systems (ESS) as one important player of the new power grids can enhance the system flexibility. It, therefore, calls for an efficient planning procedure to ensure flexibility margins by... 

Embedded Systems (ESs) have migrated from special-purpose hardware to commodity hardware. These systems have also tended to Mixed-Criticality (MC) implementations, executing applications of different criticalities upon a shared platform. Multi-cores, which are commonly used to design MC Systems (MCSs), bring out new challenges due to the Process Variation (PV). Power and frequency asymmetry affects the predictability of ESs. In this work, variation-aware techniques are explored to not only improve the reliability of MCSs, but also aid the scheduling and energy saving of them. We leverage the Core-to-Core (C2C) variations to protect high-criticality tasks and provide full service for a high... 

Due to the battery-operated nature of some embedded Mixed-Criticality Systems, simultaneous energy and reliability management is a crucial issue in designing these systems. We propose two comprehensive schemes, MC-2S and MC-4S, which exploit the standby-sparing technique to tolerate permanent faults through inherent redundancy of multicore systems and maintain the system's reliability against transient faults with low energy overhead. In these schemes, two copies of each high-criticality task are scheduled on different cores to guarantee their timeliness in case of permanent fault occurrence. To guarantee the quality of service of low-criticality tasks, in the MC-2S scheme, one backup copy... 

Due to environmental and economic advantages, cold mix asphalt (CMA) can be considered as a good alternative to conventional hot mix asphalt (HMA). Nevertheless, it has inferior performance compared to HMA, so that the application of CMA is not recommended in the surface layer of pavements subjected to high traffic volume and/or regions with very cold or hot climate. Considering the high potential of distress occurring in the CMAs, this research is aimed at investigating the effect of crumb rubber (CR) on fracture and moisture damage resistance of the CMAs. Different CR percentages were applied through two different modification methods and, then by means of Semi-Circular Bending (SCB) test,... 

This study explores the effect of Guar gum as an eco-friendly additive on concrete mechanical characteristics. In the first stage, the slump and relative humidity tests were carried out for the fresh mortar, and tensile and compressive strengths were then determined for fifteen different mixture designs with two different curing times. Further, an exponential correlation was obtained between the ultrasonic pulse velocity and the compression test results. Additionally, scanning electron microscope (SEM) was employed to assess the bond between aggregates and Guar gum. At last, the Taguchi method and ANOVA were utilized to conduct the optimum states of the mechanical characteristics of the... 

Microfluidic synthesis methods are among the most promising approaches for controlling the size and morphology of polymeric nanoparticles (NPs). In this work, for the first time, atomistic mechanisms involved in morphological changes of polybenzimidazole (PBI) NPs in microfluidic media are investigated. The multiscale molecular dynamic (MD) simulations are validated with the literature modeling and experimental data. A good agreement is obtained between the molecular modeling results and experimental data. The effects of mixing time, solvent type, dopant, and simulation box size at the molecular level are investigated. Mixing time has a positive impact on the morphology of the PBI NPs.... 

Many companies face challenges in reducing their supply chain costs while increasing sustainability and customer service levels. A comprehensive framework for a sustainable closed-loop supply chain (CLSC) network is a practical solution to these challenges. Hence, for the first time, this study considers an integrated multi-objective mixed-integer linear programming (MOMILP) model to design sustainable CLSC networks with cross-docking, location-inventory-routing, time window, supplier selection, order allocation, transportation modes with simultaneous pickup, and delivery under uncertainty. An intelligent simulation algorithm is proposed to produce CLSC network data with probabilistic... 

Accurate determination of relative permeability curves and their hysteresis is vital for reliable prediction of the performance of oil and gas reservoirs under enhanced recovery processes. Two out of the three available approaches to simulate three-phase relative permeability hysteresis are based on two-phase hysteresis. A few options (e.g., Carlson, Killough and Jargon models) are available in commercial reservoir simulators to account for hysteresis in relative permeability curves under two-phase flow. These models are based on the assumptions of water-wet state of the rocks, while most of the reservoir rocks are mixed-wet. As a result the aim of the present work is to evaluate the... 

Fracture process of fiber-reinforced concrete notched beams is investigated here. Polypropylene macrosynthetic fibers are utilized for reinforcing concrete specimens, and a high-strength mix design is used to produce strong bonds between the embossed polypropylene fibers and the cementitious matrix of beams. Considering different locations for the notch, this study focuses on bridging mechanism under different conditions using both experimental and numerical approaches. First mode of fracture occurs due to opening of crack faces. This mode of failure is simulated by imposing symmetric boundary conditions on middle-notched beams. Inducing the notch with an offset from the middle, mixed-mode... 

This paper considers a realistic multi-service system design problem in which each service type is a stochastic sequence of services provided by different units of facilities where each facility is modeled as a set of open Jackson queueing networks. The problem is first formulated as a mixed-integer nonlinear programming model, which is further simplified to a model with a smaller number of constraints. Three exact solution methods are applied to solve the amended model. The first one is a cutting-plane method, which is based on a piecewise-linear approximation. The second is based on a mixed-integer linear programming formulation, which is enhanced by valid inequalities. The third is to use...