Y. Khodadadegan

An improved model for production systems with mixed queuing priorities: an integrated simulation, AHP and Value Engineering approach

The objective of this study was to provide a scheduling solution for the mixed priority queues discipline. This simulation model integrates Analytic Hierarchy Process (AHP) and Value Engineering (VE) for modelling and assessment of complex production systems with mixed queue priorities and service discipline. In such systems, the arriving entity will be placed in the queue according to the spectrum of similar properties; this spectrum is arranged according to the entity currently being serviced. In addition, each machine is only allowed to service identical products up to a limited period and the service turn over moves clockwise.

Validation and Initial Clinical Use of Automatic Peak Skin Dose Localization with Fluoroscopic and Interventional Procedures

PURPOSE To assess the accuracy and initial clinical use of a software tool that automatically maps and records values of skin dose, including peak skin dose (PSD), administered to patients undergoing fluoroscopically guided interventional procedures. MATERIALS AND METHODS In this retrospective study, the institutional review board determined that this HIPAA-compliant study met the criteria as a quality assurance investigation. Informed consent was waived. After the initial validation and accuracy tests, distributed skin dose and PSD estimates were obtained for fluoroscopically guided interventional procedures performed in the radiology, cardiology, and gastroenterology practice areas between January and October 2011. A total of 605 procedures were performed in 520 patients (64% men; age range, 20-95 years). The accuracy of a skin dose tool to estimate patient dose distribution was verified with phantom studies by using an external dosimeter and direct exposure film. PSD distribution, PSD according to procedure type, and PSD for individual physician operators were assessed. RESULTS Calculated PSD values agreed within ±9% of that measured by using film dosimetry under the condition of matched-phantom geometry. The area receiving the highest dose (greater than 95% of peak) agreed within ±17%. Of 605 patient procedures, 15 demonstrated PSD greater than 2 Gy, with a maximum PSD of 5.6 Gy. CONCLUSION Knowledge of the patient skin dose can help direct treatment of patients who were administered relatively high skin dose and may be used to plan future procedures. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112295/-/DC1.

Modelling priority queues with dependent service discipline by computer simulation

Manufacturing processes have become more complex in the advance technology. Spectrum disciplines make a big challenge in some manufacturing and production systems that have to follow dependent sequences. This study presents a method for modelling of complex production systems with mix queue priorities and service discipline. In such systems, each group of jobs is allowed to be in service for limited amount of time. Jobs that have similar group number with the job in service will be located in the highest priority position and other groups are ranked in a queue according to spectrum discipline. The objective of this study is modelling of complex manufacturing and production systems with dependent priority queues where no closed form expression and mathematical models have been developed. A case study is presented to show applicability of the model. The approach of this study for such complex settings may be easily extended to other similar production systems.

An Agent Based Simulation for Building Energy System Modeling

Extensive research has been done on the centralized building energy system modeling and simulation. However the centralized structure is limited to study and simulate the energy interaction between different buildings at different locations. This paper reviews the building energy consumption model, energy storage system and energy generation system in the Net-zero buildings. Incorporate with the real-time price rate model, this paper develops an agent based simulation framework for distributed building energy system under uncertainty. Each sub system is developed as an agent in the simulation model, and a virtual decision agent is designed to simulate the operation strategy. The energy flow between different agents can be easily monitored from the simulation. The differences between on-peak and off-peak control are demonstrated from the simulation result.© 2010 ASME