Sharif Digital Repository

In this study, polypropylene/clay nanocomposites were prepared by melt blending method and their thermal conductivity and the thermal conductivity of polypropylene/multi-wall carbon nanotube (MWCNT) nanocomposites were investigated and modeled. It is found that the thermal conductivity of the PP/Clay and PP/MWCNT nanocomposites is increased with increasing temperature. The thermal conductivity of the nanocomposites is improved due to incorporation of nanoclay and MWCNT compared with pure PP matrix  

Non-uniform temperature distribution at horizontal pipes cross section leads to an asymmetric thermal stress. This condition would be considered as an ageing mechanism due to fatigue effect, known as thermal stratification. To evaluate this ageing mechanism, the stress analysis should be done in horizontal pipelines like surge-line connected the pressurizer to the hot leg of primary loop of NPPs by consideration of operational or transient conditions. During these conditions, the status of surge-line would be single phase or two-phase stratified flow. To estimate the equivalent stress in horizontal section of surge-line, the developed CFD model for both single and two-phase flow is coupled... 

In order to be adapted to changes in user requirements and/or the environment, many software systems need to run continuously while they evolve. Most current approaches for such dynamic reconfiguration assume that the evolved system will behave as expected and thus will be reliable if the reconfiguration is consistent. This assumption may not correspond to reality because the delivered quality estimated previously could vary due to parameter changes at runtime. To ensure that the system acts correctly in the field after the reconfiguration, reliability of changes has to be checked at runtime. Existing approaches, however, are not applicable in highly available systems due to the possibility... 

A5/1 is a stream cipher used in GSM to provide over-the-air communication privacy. Biham and Dunkelman proposed an attack on A5/1 with time complexity of 2∧(39.91) and data complexity of 2∧(21.1) known bits and memory complexity of 32 GB. In this paper, we propose an improvement on their attack. Our improvement is identification and elimination of useless states from the precomputed table. Furthermore, we propose another way for use of table in online phase of attack that causes decreasing in the time complexity to 2∧(37.89) and memory complexity decreases to half  

The prediction of interfacial turbulence characteristics is one of the still challenging of two-phase stratified flow. The evaluation of some important parameters such as interfacial heat transfer coefficient based on turbulence kinetic energy and turbulence dissipation rate in some models, intensifies the importance of turbulence flow correct simulation. High gradient of velocity and turbulence kinetic energy at the interface of two-phase stratified flow leads to a major overestimation or underestimation of flow characteristics without any special treatment. Consideration of a source function of turbulence eddy frequency at the interface is one of the common solution employed in past... 

A robust motion controller based on backstepping technique for a robotic nurse unit to assist paraplegic patients is addressed in this paper. A backstepping controller is proposed for tracking a desired trajectory in hospital environment. Simulation results are provided to validate the proposed controller. The results show satisfactory performance of the designed controller in tracking problem. Copyright © 2005 by ASME  

Effect of random signals with various powers, as current loads, on positioning and disturbance rejection problems on micro-step PID closed loop control system is addressed in this paper. Experimental results due to implementing different white noise power, speed, and a 0.3 N.m disturbance load torque show that, Random noise source changes current profile and affects the accuracy of positioning in tracking and disturbance rejection problems. Performance of the PID proposed controller under the implementation of random noise on phases of the HSM has been proved to be accurate enough even under disturbance torque acting on the system. Copyright © 2005 by ASME  

This paper gives the results of simulation and experimental investigation on the effects of random signals on the accuracy of micro-stepping control positioning. For studying and simulation of the effect of random noise signals on performance of the accurate position control systems, such as Hybrid Stepper Motors (HSMs), a micro-step driver and controlling unit using PID controller has been designed and constructed. Several parametric studies have been carried out including different white noise power and micro-step per revolution. Tracking problem for a HSM model has been simulated, and the experimental study for similar cases has been carried out by implementing the designed controller in... 

A nonlinear position controller based on backstepping control technique is proposed for a hybrid stepper motor in micro-step operation. Backstepping control approach is adapted to derive the control scheme, which is robust to parameter uncertainties and external load disturbance. Simulation results clearly show that the proposed controller can track the position reference signal successfully under parameter uncertainties and load torque disturbance rejection. Copyright © 2005 by ASME  

In this paper, design and real time experimental implementation of Fuzzy Gain Scheduling of PID controller for Hybrid Stepper Motor in Micro-stepping operation is described that was developed to track the desired positioning problem. The control problems characterized by mathematical models exhibit significant nonlinearity and uncertainty. Good performance of proposed Fuzzy PID controller are shown  

The aim of this study is to employ feedback control loops to provide a stable forward dynamics simulation of human movement under repeated position constraint conditions in the environment, particularly during stair climbing. A ten-degrees-of-freedom skeletal model containing 18 Hill-type musculotendon actuators per leg was employed to simulate the model in the sagittal plane. The postural tracking and obstacle avoidance were provided by the proportional—integral—derivative controller according to the modulation of the time rate change of the joint kinematics. The stability of the model was maintained by controlling the velocity of the body's centre of mass according to the desired centre of... 

Exceptions are an indispensable part of the software development process. However, developers usually rely on imprecise results from a web search to resolve exceptions. More specifically, they should personally take into account the context of an exception, then, choose and adapt a relevant solution to solve the problem. In this paper, we present Exception Tracer, an Eclipse plug in that helps developers to resolve exceptions with respect to the stack trace in Java programs. In particular, Exception Tracer automatically provides candidate solutions to an exception by mining software systems in the Source Forge, as well as listing relevant discussions about the problem from the Stack Overflow... 

Despite the need for change, highly available software systems cannot be stopped to perform changes because disruption in their services may consequent irrecoverable losses. Current work on runtime evolution are either too disruptive, e.g., "blackouts" in unnecessary components in the quiescence criterion approach or presume restrictive assumptions such as the "black-box design" in the tranquility approach. In this paper, an architecture-based approach, called SAFER, is proposed which provides a better timeliness by relaxing any precondition required to start reconfiguration. We demonstrate the validity of the SAFER through model checking and a realization of the approach on a component... 

We use field emission scanning electron microscope (FE-SEM) to investigate the growth of palladium colloids over the surface of thin films of WO3/glass. The film is prepared by Pulsed Laser Deposition (PLD) at different temperatures. A PdCl2 (aq) droplet is injected on the surface and in the presence of steam hydrogen the droplet is dried through a reduction reaction process. Two distinct aggregation regimes of palladium colloids are observed over the substrates. We argue that the change in aggregation dynamics emerges when the measured water drop Contact Angel (CA) for the WO3/glass thin films passes a certain threshold value, namely CA ≈ 46°, where a...