Sharif Digital Repository

Petroleum contamination of soil is a serious problem throughout the oil producer countries. Vegetation may play an important role in the biodegradation of toxic organic chemicals in soil. For petroleum compounds, the presence of rhizosphere micro flora may accelerate biodegradation of the contaminants. In a greenhouse study, petroleum contaminated soil were treated using phytoremediation . The C/N ratios and microbial populations were assessed in the beginning and the end of trials. The results showed that Puccinellia distance could tolerate the harsh condition of the soils. As MPN increases, C/N ratios decrease among trials. N, as a nutrient, had effects on both microbial populations and... 

A hot gas generator is a compact heat exchanger that produces high temperature or enthalpy gases. This paper presents two methods for controlling the system. The first one is an adaptive sliding mode controller that is a Lyapunov based method and proposed to confront the dynamic modeling deficiencies and system uncertainties. The second one is a linear adaptive controller that gives a new attractive ability to the system which can track a complicated requested path. Each of the presented controllers has some capabilities that may be preferred to other. In this paper, these methods are extensively compared by several transient inputs. On the other hand, since heat exchangers are typically... 

In this paper the question of the emission of fermions in the process of dilaton black hole evolution and its characteristics for different dilaton coupling constants α are studied. The main quantity of interest, the greybody factors, are calculated both numerically and in analytical approximation. The dependence of the rates of evaporation and behaviour on the dilaton coupling constant is analysed. Having calculated the greybody factors, we are able to address the question of the final fate of the dilaton black hole. For that we also need to perform dynamical treatment of the solution by considering the backreaction, which will show a crucial effect on the final result. We find a transition... 

In pebble bed reactors, the core is filled with thousands of graphite and fuel pebbles. Fuel pebbles in these reactors consist of TRISO particles, which are embedded in a graphite matrix stochastically. The reactor core is also stochastically filled with pebbles. These two stochastic geometries comprise the so-called double heterogeneous nature of this type of reactor. In this paper, a pebble bed reactor, the HTR-10, is used to demonstrate a treatment of this double heterogeneity using the MCNP5 Monte Carlo code and MATLAB programming. In this technique, TRISO particles are modeled in a pebble using the expanded FILL and LATTICE features of MCNP5. MATLAB is used to generate random numbers... 

The aim of this research is bonding of three-layered St/AZ31/St composite by roll-bonding process. The roll-bonding process was performed at three preheating temperatures, 340, 400 and 450°C, with thickness reduction of 30 to 68% and different thicknesses of intermediate layer (AZ31). In order to improve the bonding strength, the as-rolled specimens were annealed at constant temperature of 375°C. For evaluation of bond strength and investigating the formation of a diffusion layer, the results of peel test and microscopic images were studied. Tensile specimens were prepared along the rolling direction to measure the mechanical properties of the composite. The results showed that by increasing... 

Abstract: We consider the back reaction of the energy due to quantum fluctuation of the background fields considering the trace anomaly for Schwarzschild black hole. It is shown that it will result in modification of the horizon and also formation of an inner horizon. We show that the process of collapse of a thin shell stops before formation of the singularity at a radius slightly smaller than the inner horizon at the order of (Formula presented.). After the collapse stops the reverse process takes place. Thus we demonstrate that without turning on quantum gravity and just through the effects the coupling of field to gravity as trace anomaly of quantum fluctuations the formation of the... 

In this work, cold rolling behavior of stainless steel 304L is investigated and the effects of different process parameters on the occurrence of strain-induced martensite and mechanical properties are studied. The rolling experiments are conducted under different rolling speeds and reductions in which a set of samples is deformed at room temperature and the other set is first cooled to the temperature of − 10 °C and then rolled. Afterward, the developed microstructures and mechanical properties of the rolled steel are evaluated employing different testing techniques. In order to justify the results, mathematical modeling of cold rolling operation is also performed using Abaqus/Explicit to... 

Background: Although kinematic assessment has potentials for better evaluation of the movement quality, they are not widely used in clinics. Besides the equipment cost, the contradictory results of their clinimetric analysis are presumed as a major reason. This raises concerns about whether the current kinematic indices are intrinsically sound and truly reflect the quality of the subjects’ movement. Methods: A list of essential requirements for the kinematic indices (KIs) was proposed. Monotonic response to the change in the movement quality, independence from the task geometry and the subjects’ upper limb dimensions and speed, and robustness against the measurement error was investigated.... 

Creep mechanism and cavitation of AA5052 were studied employing creep experiments at 200–350°C and stresses 15–70 MPa. The microstructural observations were then performed to assess grain growth and formation of cavities. The apparent activation energy was defined in a range of 154–166 kJ/mole. It was found that at higher normalised stress region ((Formula presented.)), the stress exponent was about 7 and at lower stresses it decreased to about 5. Microstructural instability, that is, grain growth, was detected during creep at a temperature of 300°C or higher. This phenomenon affected the strain rate and the governing mechanisms. Microstructure of the sample tested at 300°C revealed that the... 

Lifespan of high temperature services could seriously be affected by cavitation and thus, prediction of this phenomenon is considered as a significant task. A two-dimensional cellular automata approach coupled with governing equations for cavity nucleation and growth was developed to predict the size and distribution of cavities. Different growth mechanisms including diffusion and strain-controlled processes were taken into account and also, the coalescence phenomenon and the corresponding growth rate were considered in the model. The creep experiments were conducted on AA5052 under different temperatures and applied stresses such as 15 MPa at 300 °C, 20 MPa at 300 °C and 30 MPa at 270 °C... 

Background: While motor recovery is preferred to compensatory movements for stroke patients with mild to moderate motion impairment, current movement quality assessments rarely reflect the differences between a patient's pre- and post-stroke movement patterns. Such comparison can help therapists to identify the rate of the restoration of premorbid motion patterns and prescribe the most effective treatment. Methods: This paper attempted to present a new biomechanical metric for the quality of upper-limb movements which uses the subject's optimal movements as a reference to evaluate his/her UL movement quality. To this end, an inverse optimal control algorithm was applied to find an estimation... 

We use the Fokker-Planck equation and its moment equations to study the collective behavior of interacting particles in unsteady one-dimensional flows. Particles interact according to a longrange attractive and a short-range repulsive potential field known as Morse potential. We assume Stokesian drag force between particles and their carrier fluid and find analytic single-peaked traveling solutions for the spatial density of particles in the catastrophic phase. In steady flow conditions the streaming velocity of particles is identical to their carrier fluid, but we show that particle streaming is asynchronous with an unsteady carrier fluid. Using linear perturbation analysis, the stability... 

This paper addresses a nonlinear model predictive controller design for a single-phase PFC rectifier exploiting the Sheppard-Taylor converter. After approximation of the tracking error in the receding horizon by its Taylor-series expansion to any specified order, an analytic solution to the MPC is developed and a closed-form nonlinear predictive controller is introduced. The proposed nonlinear model predictive control (NMPC) derived using approximation can stabilize the original nonlinear systems if certain conditions, which can be met by properly choosing predictive times and the order for Taylor expansion, are satisfied. The main advantage of this digital control method is that unity power...