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Selection of Simulation-Optimization Meta-Modeling Approach in Manufacturing Supply Chains
, M.Sc. Thesis Sharif University of Technology ; Ghasemi Tari, Farhad (Supervisor)
Abstract
This research presents a modified algorithm for constrained optimization of random simulation models. One output is selected as objective to be minimized, while other must satisfy the given threshold value. Moreover, the simulation inputs must be integer and satisfy linear or nonlinear constraints. The research applies a sequentialized experimental design to specify the simulation input combinations, Kriging (or spatial correlation modeling) to analyze the global simulation input/output data resulting from these designs, and nonlinear programming to estimate the optimal solution from the Kriging metamodels. In addition, a simulation model is developed for different inventory planning...
Multi-level asynchronous delta-sigma modulation based ADC
, Article ICIAS 2012 - 2012 4th International Conference on Intelligent and Advanced Systems: A Conference of World Engineering, Science and Technology Congress (ESTCON) - Conference Proceedings, 12 June 2012 through 14 June 2012 ; Volume 2 , June , 2012 , Pages 725-728 ; 9781457719677 (ISBN) ; Aghdam, E. N ; Najafi, V ; Sharif University of Technology
2012
Abstract
A Multi-level asynchronous delta sigma modulator consist of several Schmitt-triggers and a novel time-to-digital converter is presented as a core of a delta sigma modulation based analog to digital converter (ADC). The modulator firstly modulates the amplitude of its analog input signal to a multilevel asynchronous duty-cycle modulated signal. Then a time to digital converter (TDC) must be applied to generate digital representation of the received signal from the multi-level asynchronous duty-cycle modulated signal. A multi-level structure has been developed in this work while the prior works often used a single Schmitt. One of the most important limitations in conventional asynchronous...
Trunk hybrid passive–active musculoskeletal modeling to determine the detailed t12–s1 response under in vivo loads
, Article Annals of Biomedical Engineering ; Volume 46, Issue 11 , 2018 , Pages 1830-1843 ; 00906964 (ISSN) ; Arjmand, N ; Shirazi Adl, A ; Sharif University of Technology
Springer New York LLC
2018
Abstract
Biomechanical models of the spine either simplify intervertebral joints (using spherical joints or deformable beams) in musculoskeletal (MS) or overlook musculature in geometrically-detailed passive finite element (FE) models. These distinct active and passive models therefore fail to determine in vivo stresses and strains within and load-sharing among the joint structures (discs, ligaments, and facets). A novel hybrid active–passive spine model is therefore developed in which estimated trunk muscle forces from a MS model for in vivo activities drive a mechanically-equivalent passive FE model to quantify in vivo T12–S1 compression/shear loads, intradiscal pressures (IDP), centers of rotation...
Effect of changes in the lumbar posture in lifting on trunk muscle and spinal loads: A combined in vivo, musculoskeletal, and finite element model study
, Article Journal of Biomechanics ; Volume 104 , February , 2020 ; Arjmand, N ; Shirazi Adl, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Irrespective of the lifting technique (squat or stoop), the lumbar spine posture (more kyphotic versus more lordotic) adopted during lifting activities is an important parameter affecting the active-passive spinal load distribution. The advantages in either posture while lifting remains, however, a matter of debate. To comprehensively investigate the role on the trunk biomechanics of changes in the lumbar posture (lordotic, free or kyphotic) during forward trunk flexion, validated musculoskeletal and finite element models, driven by in vivo kinematics data, were used to estimate detailed internal tissue stresses-forces in and load-sharing among various joint active-passive tissues. Findings...
A UHF micro-power CMOS rectifier using a novel diode connected CMOS transistor for micro-sensor and RFID applications
, Article International Conference on Electronic Devices, Systems, and Applications ; 2012 , Pages 234-238 ; 21592047 (ISSN) ; 9781467321631 (ISBN) ; Hamidon, M. N ; Khoddam, M ; Najafi, V ; Sharif University of Technology
2012
Abstract
The design strategy and efficiency optimization of UHF micro-power rectifiers using a novel diode connected MOS transistor is presented. The proposed diode connected MOS transistor uses a new bulk connection which leads to reduce the threshold voltage and leakage current in compare to conventional diode connected transistors. Using the proposed diode in typical rectifiers makes a significant improvement in output voltage and current therefore the efficiency is increased comparing to the same rectifier architectures using conventional diodes. Also a design procedure for efficiency optimization is presented and a superposition method is used to optimize the performance of multiple output...
Position and Attitude Synchronization of Nano-Satellites Formation Flying Under J2 and Atmospheric Drag Perturbation
, M.Sc. Thesis Sharif University of Technology ; Alasty, Aria (Supervisor) ; Salarieh, Hassan (Supervisor)
Abstract
Spacecrafts formation flying is defined as tracking or keeping of desired distance, relative position and attitude of two or more spacecrafts during a maneuver. Division of tasks between various smaller spacecraft’s and so reduction of need to advanced technologies, increase in reliability in system and doing special missions like 3-D imaging of planets and combining parameter measurements are some advantages of this method. For development of this method, in this thesisin addition of reviewing the common methods in spacecraft’s formation flying, we are supposed to provide a simple and new method called distributed control for controlling a formation of spacecrafts. Additionally by providing...