Sharif Digital Repository

In this paper, the effects of different parameters on the hairiness of siro-jet spun yarns, such as the nozzle pressure, the distance between the front roller nip and inlet of the nozzle, and jet structure were investigated. Using the Taguchi method, it was concluded that the factor air pressure has the strongest effect and the factor distance between the front roller nip and inlet of the nozzle does not have a significant effect on the performance of the siro-jet spinning system in reducing yarn hairiness. A computational fluid dynamics model was developed to simulate the airflow pattern inside the jets. The effect of air pressure and the jet structure was simulated using Fluent 6.3... 

Different analysis methods have been used for voltage stability assessment. In comparison with static analysis methods, little work has been done on dynamic analysis of large interconnected power systems. Voltage instability can be studied effectively with a combination of static approaches and time simulations. This paper discusses voltage stability assessment using mixed static and dynamic techniques. Using static methods, a voltage stability based ranking is carried out to specify faint buses, generators and links in power system. The system is analyzed for most severe conditions. Then, time domain simulation is performed for the conditions determined by voltage instability ranking. The... 

In the present research, proton exchange membranes based on partially sulfonated poly (ether sulfone) (S-PES) with various degrees of sulfonation were synthesized. It was found that the increasing of sulfonation degree up to 40% results in the enhancement of water uptake, ion exchange capacity and proton conductivity properties of the prepared membranes to 28.1%, 1.59 meq g -1, and 0.145 S cm -1, respectively. Afterwards, nanocomposite membranes based on S-PES (at the predetermined optimum sulfonation degree) containing various loading weights of organically treated montmorillonite (OMMT) were prepared via the solution intercalation technique. X-ray diffraction patterns revealed the... 

We present an asymptotically convergent nonlinear attitude estimator using a rate gyro and GPS. Double-difference (DD) carrier phase measurements are provided by at least two GPS antennas. The unknown integer ambiguity factor related to GPS carrier phase measurement is estimated along with the attitude. An observability condition is derived to guarantee the convergence of the estimator when a single baseline vector is available with more than four satellites in view. A systematic procedure for tuning observer parameters is also presented. Finally, the experimental test from a light fixed-wing aircraft illustrates the performance of the proposed observer. © 1993-2012 IEEE  

This paper presents an asymptotically-convergent nonlinear attitude estimator for rigid bodies using a rate gyro and GPS. Double-difference carrier phase measurement are provided by at least two GPS antennas. The unknown integer ambiguity factor related to GPS carrier phase measurement is estimated along with the attitude. An observability condition is derived to guarantee convergence of the estimator when a single baseline vector is available with more than four satellites in view. Finally, experimental test from a survey boat illustrates performance of the proposed observer. © 2018 IEEE  

Sludge handling is a common issue in all biological wastewater treatment methods. In this study, sonication technique as a state-of-the-art technology has been applied to a continuous MBBR system with the aim of sludge reduction. A novel configuration of MBBR with an additional recycle stream of sonicated sludge was used as the experimental setup. Based on exposed energy and sludge disruption performance, optimized sonication density and exposure time were obtained 1.5 W/mL and 15 min, respectively. This condition provided 42.2% increase in soluble COD as a result of sludge disintegration. Our results revealed that the performance of MBBR and excess sludge reduction were affected by... 

A modified two-surface critical state plasticity model for saturated and unsaturated soil is presented in this study. The key modification in new model is inclusion of an alternative yield surface used to simulate the behavior of unsaturated soils in addition to corresponding saturated conditions. Moreover, a numerical technique is used to obtain an incremental stress–strain response from loading curves. Modification is applied continuously in each incremental step to return the final stress states and hardening parameters to the yield surface. Results revealed that the adopted modeling approach can predict two independent sets of laboratory unsaturated experiments under various conditions... 

Nanocomposites containing ZrO2 and HA have been considered in various fields due to their unique mechanical properties. The principal purpose of this paper is to select the models with the maximum accuracy for the prediction of microhardness of CHA/ZrO2 nanocomposite. For this purpose, three models, including gene expression programming (GEP), gray wolf optimization algorithm (GWOA), and least squares support vector machine (LS-SVM), were implemented to predict and optimize the microhardness of the CHA/ZrO2 nanocomposite. Finally, the results showed that the data obtained from the LS-SVM model were closer to the preliminary data than the others. According to the results, the LS-SVM could... 

This paper presents the results of a thorough analysis of applying power quality standards to a granite factory. It explains the procedure of determining power quality indices in a power system. The paper presents the field data and provides the results of statistical analysis in order to extract power quality indices. A comparison against standard limits is also given. The case study gives an overview of power quality in such customers and brings up some practical limitations when applying power quality standards. ©2006 IEEE  

Titanium carbonated hydroxyapatite (Ti/CHA) nanobiocomposites have extensive biological applications due to the excellent biocompatibility and similar characteristics to the human bone. Ti/CHA nanobiocomposite has good biological properties but it suffer from diverse characteristics especially in hardness, Young's modulus, apparent porosity and relative density. This investigation is an attempt to propose the predictive models using gene expression programming (GEP) to estimate these characteristics. In this regards, GEP is used to model and compare the effect of practical variables including pressure, Ti/CHA contents and sintering temperature on their monitored properties. To achieve this... 

Cerebellum has been assumed as an array of adjustable pattern generators (APGs). In recent years, electrophysiological researches have suggested the existence of modular structures in spinal cord called motor primitives. In our proposed model, each "adjustable primitive pattern generator" (APPG) module in the cerebellum is consisted of a large number of parallel APGs, the output of each module being the weighted sum of the outputs of these APGs. Each spinal field is tuned by a coefficient, representing a descending supraspinal command, which is modulated by ith APPG correspondingly. According to this model, motor control can be interpreted in terms of the modification of these coefficients.... 

This paper proposes a decentralized market-based model for long-term capacity investment decisions in a liberalized electricity market. Investment decisions are fundamentally based on total revenues gained by investors. In most electricity markets, the complementary mechanisms are designed to ensure a desired level of reliability while covering investment costs of the suppliers. In such an environment, investment decisions are highly sensitive to expectation of price signals in both of energy market and capacity mechanisms. In this work, the system dynamics concepts are used to model the structural characteristics of electricity market such as, long-term firms' behavior and relationships... 

The advent of agile methodologies, though contributing much to software development processes, had a more profound impact on project management processes. Through supporting adaptability in their process frameworks, agile methodologies deviated from conventional project management approaches. This novel attitude has resulted in the emergence of an agile framework for project management. The Agile Project Management Framework (APMF) consists of fine-grained project management practices applied in agile methodologies, and is fast emerging as an alternative to the conventional project management framework. However, there are deficiencies in both frameworks that prevent developers from enhancing... 

Catalysts as the dynamo of chemical reactions along with solvents play paramount roles in organic transformations in long-lasting modes. Thus, developing effective and biobased catalysts in nontoxic solvents is highly in demand. In this report, carbon quantum dots (CQDs) functionalized with-lysine (Lys-CQDs) were generated from entirely nature-derived materials; they were demonstrated to be a promising catalyst for C-N bond formation in choline chloride urea (ChCl/U), a natural deep eutectic solvent (NADES). Among a number of synthesized CQDs, Lys-CQD turned out to be a powerful catalyst in the model reaction with aniline to afford phenyl urea. This type of transformation is important... 

Purpose: The nanofluid flow and heat transfer within a heat exchanger, with different thermal arrangements of internal active bodies, are investigated. Design/methodology/approach: For the numerical simulations, the lattice Boltzmann method is utilized. The KKL model is used to predict the dynamic viscosity of CuO-water nanofluid. Furthermore, the Brownian method is taken account using this model. The influence of shapes of nanoparticles on the heat transfer performance is considered. Findings: The results show that the platelet nanoparticles render higher average Nusselt number showing better heat transfer performance. In order to perform comprehensive analysis, the heatline visualization,... 

The influence of annealing treatment on macro- and micro-texture of cold-rolled FeCo-7.15V ferro-magnetic ultra-thin foils were studied. The microstructural studies performed by field emission scanning electron microscope (FE-SEM) showed the formation of paramagnetic precipitations ((Fe, Co)3V) during annealing. During cold rolling of the FeCo-7.15V magnet, the texture components of type (113)[110], (001)[110], (111)[110], and (111)[121], all related to α and γ-fibers were formed. X-ray diffraction (XRD) and local texture measurements performed by electron backscatter diffraction (EBSD) were made on the annealed samples. Both methods revealed that the recrystallized samples have texture... 

The numerical modeling of natural convection fluid flow and heat transfer in a quarter of gearwheel-shaped heat exchanger is carried out. The heat exchanger is included with internal active square bodies. These bodies have hot and cold temperatures with different thermal arrangements. Three different thermal arrangements are considered and showed with Case A, Case B and Case C. The CuO-water nanofluid is selected as operating fluid. The Koo-Kleinstreuer-Li (KKL) correlation is utilized to estimate the dynamic viscosity and thermal conductivity. In addition, the shapes of nanoparticles are taken account in the analysis. The Rayleigh number, nanoparticle concentration and thermal arrangements...