Sharif Digital Repository

Since the advent of conventional activated sludge biological treatment plants, their low efficiency in nitrogen and phosphorus removal has become a significant concern. Therefore, in this study, the performance of microalgal-activated sludge membrane bioreactor (MAS-MBR) as a self-biological treatment or as a post-treatment for conventional biological treatments was investigated. A continuous MAS-MBR with two ratios of algae/sludge (only microalgae and 5:1) was used to treat raw and treated wastewater. The optimum case was achieved with the cultivation of mixed algae/sludge in raw wastewater (R2 case). In this case, the ammonium and phosphorus removal efficiencies were 94.36 ± 3.5 and 88.37... 

In this paper, results of an investigation on strain hardening mechanisms of aged AEREX350 alloy during room temperature compression testing are reported. TEM studies were conducted on commercial samples aged at 850 °C both before and after deformation in a strain range of 0.15-0.27. It was found that only coherent γ′ precipitates with L12 structure formed in these samples prior to deformation. TEM studies also showed twin intersections in the deformed samples. Based on these observations, it is suggested that the high strain hardening rate of the aged material in this strain range is mainly related to the formation of intersecting deformation twins. This is attributed to the decrease in the... 

Understanding and investigation of a high-speed craft dynamics, their longitudinal dynamic instabilities in calm water and behavior in waves are of a great importance. Determination of motion equation coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Therefore, it could be useful in controlling the vessel instabilities. The main purpose of this research is to determine the coefficients of longitudinal motions of a planing catamaran using computational fluid dynamics (CFD) and evaluating the interceptor effect on hydrodynamic coefficients of that, which is widely utilized in controlling the motions of a high-speed... 

Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using RANS method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly, and requires meticulous laboratory equipment; therefore, utilizing numerical methods and developing a virtual laboratory seems highly efficient. In the present study, the... 

Determination of high-speed crafts' hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using Reynolds-averaged Navier-Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly... 

Schramm-Loewner evolution (SLE) is a stochastic process that helps classify critical statistical models using one real parameter K. Numerical study of SLE often involves curves that start and end on the real axis. To reduce numerical errors in studying the critical curves which start from the real axis and end on it, we have used hydrodynamically normalized SLE(K,P) which is a stochastic differential equation governing such curves. In this paper, we directly verify this hypothesis and numerically apply this formalism to the domain wall curves of the Abelian sandpile model (K= 2) and critical percolation (K= 6). We observe that this method is more reliable than previously used methods in the... 

Avalanche frontiers in Abelian sandpile model (ASM) are random simple curves whose continuum limit is known to be a Schramm-Loewner evolution with diffusivity parameter κ=2. In this paper we consider the dissipative ASM and study the statistics of the avalanche and wave frontiers for various rates of dissipation. We examine the scaling behavior of a number of functions, such as the correlation length, the exponent of distribution function of loop lengths, and the gyration radius defined for waves and avalanches. We find that they do scale with the rate of dissipation. Two significant length scales are observed. For length scales much smaller than the correlation length, these curves show... 

In the band structure analysis of photonic crystals it is normally assumed that the full photonic gaps could be found by scanning high-symmetry paths along the edges of Irreducible Brillouin Zones (IBZ). We have recently shown [1] that this assumption is wrong in general for sufficiently symmetry breaking geometries, so that the IBZ is exactly half of the complete BZ. That minimal required symmetry arises from the requirement on time-reversal symmetry. In this paper we show that even that requirement might be broken by using gyro-magnetic materials in the composition of photonic structures we can observe that the IBZ extends fully to the boundaries of the complete BZ, that is IBZ must be as... 

Tensile and room temperature Charpy V-notch impact tests along with microstructural studies were used to evaluate the variations in the as-cast mechanical properties of low-carbon steels with and without vanadium and niobium. Tensile test results indicate that good combinations of strength and ductility can be achieved by microalloying additions. While the yield strength and UTS increase up to respectively 370-380 and 540-580 MPa in the microalloyed heats, their total elongation range from 20 to 25%. TEM studies revealed that random and interphase fine-scale microalloy precipitates play a major role in the strengthening of the microalloyed heats. On the other hand, microalloying additions... 

Association mapping of genetic diseases has attracted extensive research interest during the recent years. However, most of the methodologies introduced so far suffer from spurious inference of the associated sites due to population inhomogeneities. In this paper, we introduce a statistical framework to compensate for this shortcoming by equipping the current methodologies with a state-of-the-art clustering algorithm being widely used in population genetics applications. The proposed framework jointly infers the disease-associated factors and the hidden population structures. In this regard, a Markov Chain-Monte Carlo (MCMC) procedure has been employed to assess the posterior probability... 

In general, decomposition methods can facilitate the process of solving sophisticated and heterogonous problems in the area of software development and engineering. These approaches are assisting to decompose problems based on different disciplines, characteristics and functionalities that is results into increasing the computational efficiency (e.g. parallel processing/computing) and accelerate the software changing process, software modifications and error tracking. Essentially, these approaches contribute to the degree of modularity to decompose a complex problem into different sub-problems and to focus on local objectives. There are different approaches that are used to decompose a... 

The unpredictable nature and devastating impact of earthquakes enforce governments of disaster-prone regions to provide practical response plans to minimize damage and losses resulting from earthquakes. Logistics management is one of the key issues that should be considered for an appropriate response, in particular, the planning of the transport of commodities required during response and the evacuation of injured people. This paper develops a dynamic model for dispatching and routing vehicles in response to an earthquake. We focus on the transport of both commodity towards affected areas and injured people to hospitals. The proposed model is capable of receiving updated information at any... 

Ultrafine-grained Al-CNT (2 and 4 vol%) composites were successfully fabricated using the flake powder metallurgy and hot pressing route, and the microstructure and tribological properties of the produced composites were studied. The results showed that the coefficient of friction and the wear rate of Al decrease with the addition of the CNT reinforcement. A carbon-rich film formed on the worn surfaces during wear test, which prevented the Al oxidation and yielded the self-lubricating effect for the composites. This improvement in the wear behavior of the composites can be attributed to the simultaneous effects of the ultrafine-grained matrix and strengthening and self-lubricating properties... 

A resource investment problem with discounted cash flows is a project scheduling problem in which the availability levels of the resources are considered decision variables and the goal is to find a schedule and resource requirement levels such that the net present value of the project cash flows optimizes. In this paper, we present a genetic algorithm to solve this problem. We explain the elements of the algorithm such as chromosome structure, fitness function, crossover, mutation, and local improvement operations and solve more than 220 problems with known optimal solutions to evaluate the performance of the proposed algorithm. The results of the experimentation are quite satisfactory. ©... 

A resource investment problem is a project-scheduling problem in which the availability levels of the resources are considered as decision variables and the goal is to find a schedule, and resource requirement levels, such that some objective function optimizes. In this paper, we consider a resource investment problem in which the goal is to maximize the net present value of the project cash flows. We call this problem as Resource Investment Problem with Discounted Cash Flows (RIPDCF) and we develop a heuristic method to solve it. Results of several numerical examples show that the proposed method performs relatively well  

In this work, the rheological changes of several crude oil samples exposed to ultrasonic waves for different time intervals in addition to the effect of temperature on viscosity behavior of heavy crude oils were investigated using a series of steady shear flow and oscillatory tests. The colloidal structural evolutions of flocs in oil samples were illustrated by analysis of the size distribution of flocculated asphaltene particles (confocal microscopy tests). The rheological investigations indicate that the ultrasonic irradiation dissolved heavy components in crude oil. After ultrasonic treatment, the Kouh-e-Mond crude oil was found to be pseudoplastic. In addition, confocal microscopy... 

In this article, smoothed particle hydrodynamics method is applied in order to study the free surface flow generated by two-dimensional planing flat plate. For this purpose, a two-dimensional smoothed particle hydrodynamics code is developed and validated by the well-known dam breaking problem. Four trim angles and three different velocities are considered to perform a parametric study to examine their physical effects. The obtained results from smoothed particle hydrodynamics are compared against the corresponding Reynolds-averaged Navier Stokes solutions. It is observed that at lower velocities, there exists a good agreement between the smoothed particle hydrodynamics and Reynolds-averaged... 

In this paper, CuInSe 2 (CIS) nanostructures have been synthesized via a solvothermal method using diethyamine as a solvent. Various morphologies of CuInSe 2 were obtained from the reaction of cupric chloride, indium chloride and selenium powder by changing the solvothermal conditions. The effect of the experimental parameters such as reaction time, temperature and concentration of the selenium powder were studied. The crystalline structures and morphologies of the products were characterized by means of X- ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) techniques, respectively. The results show that the morphology and dimensions of the CIS nanostructures... 

In this paper we define some stochastic perturbations of the BTW model which make it into Manna model. These models have a continuous parameter p, where p = 0 and 1 correspond to the BTW and Manna models respectively. We have investigated the properties of the statistical observables of the waves of avalanches for various values of p. Our data supports the expectation of a crossover in such systems; at large scales Manna model is dominant. Therefore we find strong evidence in favor of the universality classes being distinct. Also it is observed that the BTW fixed point is unstable when Manna-type perturbation is added to the model  

In the present paper we investigate the problem of water propagation in 2 dimensional (2D) petroleum reservoir in which each site has the probability p of being occupied. We first analyze this propagation pattern described by Darcy equations by focusing on its geometrical features. We find that the domain-walls of this model at p=pc ≃ 0.59 are Schramm-Loewner evolution (SLE) curves with κ=3.05 ∓ 0.1 consistent with the Ising universality class. We also numerically show that the fractal dimension of these domain-walls at p=pc is Df ≃ 1.38 consistent with SLEκ=3. Along with this analysis, we introduce a self-organized critical (SOC) model in which the water movement is modeled by a chain of...