Sharif Digital Repository

Molecular dynamics simulations are carried out to investigate the manipulation of metallic clusters on double-layer surfaces. The system parts are made of transition metals. The conditions which are subjected to change in the tests are material combinations for cluster, main substrate and lubricant layer (adlayer). In addition to qualitative observations, two criteria which represent the particle deformation and substrate abrasion are utilized as evaluation tools and are computed for each case. Obtaining this sort of knowledge is highly beneficial for further experiments in order to be able to plan the conditions and routines, which guarantee better success in the manipulation process  

Based on the fact that the manipulation of fine nanoclusters calls for more precise modelling, the aim of this paper is to conduct an atomistic investigation for interaction analysis of particle-substrate system for pushing and positioning purposes. In the present research, 2D molecular dynamics simulations have been used to investigate such behaviours. Performing the planar simulations can provide a fairly acceptable qualitative tool for our purpose while the computation time is reduced extremely in comparison to 3D simulations. To perform this study, Nose-Hoover dynamics and Sutton-Chen interatomic potential will be used to investigate the behaviour of the aforementioned system. Pushing of... 

Molecular dynamics simulations are carried out to investigate the manipulation of metallic clusters on stepped surfaces. Five surface forms are considered in the simulations. The system parts are made of pure transition metals and Sutton-Chen many-body potential is used as interatomic potential. The conditions which are subjected to change in the tests include: materials used for particles and substrate, and surface step conditions. In addition to qualitative observations, two criteria which represent the particle deformation and substrate abrasion are utilized as evaluation tools and are computed for each case. Simulation results show the effect of the aforementioned working conditions on... 

In this study, the artificial neural network (ANN) was used for the prediction of WDT. The inputs to network are molar mass and pressure, and the output is WDT at each input. A two-layer network with different hidden neurons and different learning algorithms such as LM, SCG, GDA and BR were examined. The network with 16 hidden neurons and Levenberg-Marquardt (LM) train function showed the best results in comparison with the other networks. Also, the predicted results of this network were compared with the thermodynamic models and better accordance with experimental data for ANN was concluded  

In this study, 40% CaO/γ-Al2O3 catalyst was used for biodiesel production from corn oil. A transesterification reaction was done for 5h at a temperature of 65°C in the presence of corn oil, methanol (methanol to oil molar ratio of 12:1), and CaO/γ-Al2O3 catalyst (0.06g/g (6wt%)). Catalyst used in this study was synthesized using the sol-gel method. In this method, two parameters of gelation temperature and nitric acid concentration were used as variables in the catalyst synthesis step, and experiments were designed using central composite design (CCD). The results indicate that the optimal point is achieved at a gelation temperature of 70°C and... 

Transesterification reaction was performed in the presence of soybean oil, methanol, and Demineralized water plant sedimentation catalyst at 60°C for 8 h in this study. Central composite design method was used to study the effect of catalyst concentration and methanol to oil molar ratio on purity and yield of produced biodiesel. The results showed catalyst concentration of 9.08 wt% and methanol to oil molar ratio of 22.49 as the optimum condition in which the values of purity and yield of the produced biodiesel in the second-order models were 99.89% and 81.83%, respectively. Experiments are in good agreement with the mentioned values as corresponded values are 99.95% and 86.68%,... 

Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

Due to international competition and strict limitations of standards regarding the noise level, investigation of gear vibration is of great importance. In this paper, nonlinear oscillations of spur gear pairs including the backlash nonlinearity is studied. Dynamic system is described through the classical single degree of freedom (SDOF) model in terms of dynamic transmission error (DTE). Using multiple scale method, forced vibration responses of the gear system including primary, super-harmonic and sub-harmonic resonances are investigated. In each case, the jump phenomenon and stability analysis are studied. In addition, the effect of dynamic and manufacturing parameters of the gear system... 

In this paper, nonlinear oscillation of the automobile gear system is studied. The backlash dynamic parameter is included in the nonlinear mathematical modeling of the problem. Using multiple scale method, forced vibration responses of the gear system including Primary, Subharmonic and Super-harmonic resonances are investigated. In each case, the jump phenomenon and stability analysis are studied. In addition, the effect of dynamic and manufacturing parameters of the gear system on the time responses are analyzed. Simulation and nonlinear analysis of the problem are developed in MAPLE and MATLAB environments  

Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

To achieve a cost-effective and reliable use of wind power generation, advanced control techniques are required. In this paper, the application of two control strategies for the improvement of wind turbine power output is investigated in the presence of model/environmental uncertainties. Rotational speed of the wind turbine and consequently its power output are controlled via manipulation of blades pitch angle (at a constant generator torque). First, the classical PID controller is designed based on root locus analysis while in the second scheme, an H∞-robust controller is designed via μ-synthesis based on DKiteration algorithm. Performance of the two controllers in tracking of the desired... 

Performance control of a boiler–turbine unit is of great importance due to demands for the economical operations of power plants and environmental awareness. In this paper, an optimal control strategy is designed to achieve the desired performance of a boiler–turbine unit. A multivariable nonlinear model of a utility boiler–turbine unit is considered. By manipulation of valves position for the fuel, steam and feed-water flows; output variables including the drum pressure, electric output and fluid density (and consequently drum water level) are controlled. Performance measure of the problem is defined such that the control efforts are minimized while the tracking objectives are obtained. In... 

In this research, nonlinear dynamics of an air-ehandling unit (AHU) is studied for tracking objectives, in the presence of harmonic perturbations. Three arbitrary realistic set-paths are considered for the indoor temperature and relative humidity. Two controllers based on feedback linearization (FBL) and pole placement approaches are designed to preserve the dynamic system around the desired tracking paths. It is shown that FBL controller works efficiently in bifurcation control and transforms the quasi-periodic limit cycles into the periodic ones (and consequently comfortable indoor conditions). In addition, FBL controller guarantees suppression of larger periodic limit cycles into the... 

Scheduling of the maintenance activities is considered, in which the duration of activities is uncertain, delivery date of the maintenance shutdown is predefined, and activities are multi-mode. The problem is a multi-mode time-constrained project scheduling problem (MTCPSP). The glycol regeneration unit in a gas refinery is as the case study. Based on the effect of equipment or sub-equipment on the system reliability, the importance value of equipment and sub-equipment within the system is determined, and these values are used in a heuristic algorithm as a priority rule for choosing activities in the schedule. Outcomes demonstrate the performance of the algorithm in early or on time delivery... 

The problem of this paper deals with the multi-mode project scheduling problem under uncertainty of activity duration where only the renewable resources are taken into account and a given deadline has to be met at the cost of recruiting additional resources. A heuristic algorithm is employed to solve this problem, and to maintain the robustness of the baseline schedule, the concept of critical chain project management (CCPM) is applied in which a new definition to resource buffer is considered. A simulation methodology is used to determine the size and location of resource buffers in the schedules in which three different buffer sizes and three different uncertainty levels are considered.... 

We design a quasi-one-dimensional spin chain with engineered coupling strengths such that the natural dynamics of the spin chain evolves a single excitation localized at the left-hand site to any specified single-particle state on the whole chain. Our treatment is an exact solution to a problem which has already been addressed in approximate ways. As two important examples, we study the W states and Gaussian states of arbitrary width. © 2019 American Physical Society  

Monthly mean satellite derived Chl-a, aerosols, wind, SST, PAR, and turbidity datasets were used to investigate the possible factors regulating phytoplankton variability in the Persian Gulf. The spatial correlation analysis revealed two distinct regions of SST and PAR, and a relatively uniform spatial correlation pattern of the other parameters. The cross correlation between aeolian dusts and Chl-a was significantly positive with 1–3 months offset. The pattern of spatial correlation between Chl-a and SST was positive in the shallow regions without time lag, and was negative with time offset of 3–5 months in deeper regions. The cross correlation between Chl-a and north-ward winds were... 

Early diagnosis of lung cancer is very important in improving patients life expectancies. Due to the high number of Computed Tomography (CT) images, fast and accurate diagnosis is difficult for radiologists. Therefore, there is an increasing demand for Computer-Aid Diagnosis (CAD) lung cancer. The core of all lung cancer detection systems is the distinction between cancer and non-cancerous tissues. This operation is performed in the false positive reduction phase, which is one of the most critical part of the lung cancer detection systems. The primary objective of this paper is to present a new method based on 3D Convolutional Neural Networks (CNN) that can reduce the false positives rate... 

There are several critical measures in the project performance evaluation such as time, cost, and quality. In this paper, a new method for project performance evaluation is presented by combining the project Golden Triangle and the methods in decision science. At first, strategies and measures are introduced for the perspectives of the Balanced Scorecard (BSC) method according to their effect on time, cost, and quality. Next, the Analytic Hierarchy Process (AHP) method is used to weigh the measures by the judgments of experts after integrating AHP and BSC. Then, the weights of the five project phases - from the initiation to the closure - are calculated by the Technique for Order of...