Sharif Digital Repository

The increase of pollution and the expansion of industrial, agricultural wastewater and urban runoff discharges in water sources have intensified the concentration of water pollutants. Considering that in Iran as in other countries the major part of drinking water is obtained from surface waters and due to the importance of disinfection, chlorination is doubtlessly the optimum and most common water treatment method used. However this method produces chlorination by-products (CBPs). Trihalomethanes(THMs) and Haloaceticacids (HAAs) are the main and most important groups of disinfection by-products (DBPs). Separation of THMs has gained a lot of breakthroughs since a lot of time elapses from its... 

A precise thermal-hydraulics model is of great importance for developing more effective designs of High Temperature Gas Cooled Reactors (HTGR). Recently, several advancements have been made in the methods of analysis of porous media which could be of significant value in the development of more precise and robust codes. The objective of this research is to incorporate some of the most recent improvements in the development of a new 2D program for thermal-hydraulics analysis of modular high temperature reactors. The program is mainly based on the solution of a coupled set of mass, energy and momentum conservation equations for the gas flow, along with the energy conservation equation in the... 

The current study aims at introducing a 2D and fast-running code for the issues pertinent to design, analysis and safety in modular high temperature reactors. While the porous media approach is only applied to pebble bed type, the analysis in this paper covers both pebble bed and prismatic reactor. A time-dependent mass equation along with energy conservation equation for the cooling gas and a time-dependent energy conservation equation for the solid was solved. Appropriate series of constitutive equations (e.g. heat transfer coefficient, effective heat conductivity of solid, heat transfer coefficient, pressure drop etc.) has been recruited as well. In addition a finite-volume method is... 

Let δ be a (d-1)-dimensional simplicial complex and let h(δ)=(h0,h1,...,hd) be its h-vector. A recent result of Murai and Terai guarantees that if δ satisfies Serre's condition (Sr), then (h0,h1,...,hr) is an M-vector and hr+hr+1+...+hd is nonnegative. In this article, we extend the result of Murai and Terai by giving r extra necessary conditions. More precisely, we prove that if δ satisfies Serre's condition (Sr), then iihr+i+1ihr+1+...+i+d-rihd, 0≤i≤r≤d, are all nonnegative  

In this paper, electrical wire explosion (EWE) was used as a simple, clean, in situ method to synthesise nano zero-valent iron (nZVI) particles in liquid mediums. The structural and physical properties of the synthesised nZVI particles were characterised by x-ray diffraction, Brunauer–Emmett–Teller analysis, field emission scanning electron microscopy and transmission electron microscopy. The synthesised spherical nanoparticles, at a specific size of 10–50 nm, possessed large surface areas of approximately 13.27 m2/g, reinforcing the significant advantages of EWE, that is, less aggregation and in situ production of nanoparticles with enhanced removal efficacy, for groundwater treatment.... 

Shear lag phenomenon has long been taken into consideration in various structural codes; however, the AISC provisions have not proposed any specific equation to calculate the shear lag ratio in some cases such as fillet-welded connections of front-to-front double channel sections. Moreover, those equations and formulas proposed by structural codes are based on the studies that were conducted on riveted and bolted connections, and can be applied to single channel sections whilst using them for fillet-welded double channels would be extremely conservative due to the symmetrical shape and the fact that bending moments will not develop in the gusset plate, resulting in less stress concentration.... 

A great amount of work has been done over the past few years to understand the structure-properties relationship in polypropylene/glass fiber composites. This is because of the very fast-growing rate of polypropylene applications in the automotive and other industries. This work focused on the role of glass fibers and fiber-matrix adhesion on deformation mechanism. Composites with different fiber content, with and without adhesion promoter, were fabricated. Tensile tests and microscopy techniques were conducted. Based on the results, a physical model has been proposed that illustrates the initiation and growth of the damage under static loading condition. According to this work, the... 

Gas pressure reduction stations are essential in energy distribution networks because even a minor failure of these systems causes disruptive consumer problems. This study aims to introduce and implement a new knowledge-based platform that uses the synthesized expert's opinions to improve gas pressure control facilities. Given the record of failure of gas transmission system components and the data's uncertain nature, a new fuzzy expert system is developed that takes advantage of the object-oriented programming paradigm to analyze failure modes and conditions. The artificial intelligent model is designed in C# programming language, and a user-friendly interface is developed for ease of... 

In the present research the aging behavior of Al6061 alloy and Al6061/SiCp composite fabricated by powder metallurgy method was investigated. The solution treatment of the samples were carried out at 527°C for 2, 3and 4 h followed by aging at 180°C for different aging times between 1 and 10 h. The existence of SiC particles led to increasing the peak hardness of the composite. The peak hardness of the composite took place at shorter times than that of the 6061 alloy for the samples solution treated for 3and 4 h, but took place at longer times for the samples solution treated for 2 h. The optimum solution treating time was about 3 h for both the composite and the 6061 alloy that led to the... 

Let F be a field, char (F) ≠ 2, and S ⊆ GLn (F), where n is a positive integer. In this paper we show that if for every distinct elements x, y ∈ S, x + y is singular, then S is finite. We conjecture that this result is true if one replaces field with a division ring. © 2009 Elsevier Inc. All rights reserved  

Gradual chemical (displacement) reaction between CuO and Al powders during high-energy attrition milling under a high purity argon atmosphere was studied. Differential thermal analysis (DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were employed to study the solid-state reaction. It was shown that the solid-state reaction occurred during mechanical alloying (MA) and resulted in the dissolution of copper into the aluminum lattice and formation of nanometric alumina particles. The reinforcement particles were mostly distributed at the grain boundaries of Al matrix with an average crystallite size of about 50 nm. In DTA curve of the milled powders, a small... 

Different structures of dye-sensitized solar cells (DSCs) were fabricated with various compositions and arrangement modes of the photoanodes. The solvothermally grown TiO2 nanoparticles and sol-gel derived spherical TiO2 and BaTiO3 particles were employed as the active and scattering layers of DSCs. TiO2 nanoparticles and spherical particles had pure anatase structure with particle size of 15-30 nm and 200-400 nm, respectively, whereas 300-800 nm BaTiO3 particles showed cubic perovskite structure. The efficiency improvement of mono-layer cells made of TiO2 nanoparticles (i.e., 7.22%) was achieved by light harvesting mechanism. Further enhancement of photovoltaic performance was achieved by... 

Simulation has been shown to be one of the most powerful tools in many areas of the health-care system, a system which attracted the attention of researchers due to its intricacy. The main goal of this study is to evaluate the patients' flow in an emergency department (ED). Discrete event simulation (DES)has been used as the core of this research so that it offers various ways to reduce the length of stay (LOS)of patients in different segments of ED by assessing various scenarios. In particular, a new approach for verification of the simulated model will be discussed. This study reports on the results that extracted from a case study on patient record data in one of the EDs located in Tehran... 

In last decades, rubber-toughened polymer blends have been the object of considerable interest by many investigators, owing to their attractive mechanical as well as physical properties. Polypropylene (PP) is a type of polyolefin which can be toughened using rubber particles. In another paper [J. Appl. Polym. Sci., submitted for publication], the role of ethylene-propylene (EPR) particles on the deformation mechanism during tensile tests and the fracture mechanism under quasi-static loading tests has been investigated. This paper is instead focused on the role of EPR particles on the fracture mechanism under dynamic loading (impact properties) of EPR/PP blends. Blends with different weight... 

In recent decades, great attention has been devoted to the toughening of isotactic poly(propylene) (PP) with elastomers such as ethylene-propylene rubber (EPR). The most important reasons for this interest are the moderate cost and favorable properties of PP. This article is focused on the role of EPR in the deformation and fracture mechanism of PP/EPR blends with different volume fractions of elastomer phase. Differential scanning calorimetry (DSC), tensile tests, and microscopy techniques were used in this study. The fracture mechanism of isotactic PP toughened by EPR (PP/EPR) has also been studied by three point bending (3-PB) and four point bending (4-PB) tests. Rubber particle... 

Let I be a monomial ideal in the polynomial ring S=K [x1,... xn]. We study the Stanley depth of the integral closure Ī of I. We prove that for every integer k ≥ 1, the inequalities (S/Ik) ≤ sdepth (S/Ī) and sdepth(Ik) ≤ sdepth(Ī) hold. We also prove that for every monomial ideal I⊂ S there exist integers k1,k2≥ 1, such that for every s≥ 1, the inequalities sdepth (S/Isk1) ≤ sdepth(S/Ī) and sdepth (Isk2) ≤ sdepth (Ī) hold. In particular, mink{sdepth(S/Ik)} ≤ sdepth(S/Ī) and min̄k {sdepth (Ik)}≤ sdepth(Ī). We conjecture that for every integrally closed monomial ideal I, the inequalities sdepth(S/I)≥ n-l (I) and sdepth (I)≥ n-l (I)+1 hold, where l (I) is the analytic spread of I. Assuming the... 

Damage tolerance improvement has been reported by laminating aluminum alloys and composites by researchers. Three-layer laminates comprising Al6061 outer layers and Al1050 interlayer have been roll bonded in this research. While most of the works done have focused on fracture properties of roll bonded Al laminates in crack arrester geometry, this study explores their behavior in crack divider configuration. Rolling strain is varied to control the interfacial bonding in laminates. The fracture behavior of laminates and the constituent material was examined via three-point bending and impact tests. This study presents significant improvement in damage tolerance of laminates compared to their... 

In this work, the feasibility of friction stir lap welding an aluminium alloy (Al-5083) to the aluminium clad steel sheet was studied. The welded joints were characterised by various methods including shear-tensile test and optical microscopy and scanning electron microscopy. The results indicated that sound and defect free joints were obtained. The fracture loads of the samples reached up to 94% compared with that of the steel base metal. Moreover, the joint strength linearly increased with the decrease in thickness of the aluminium layer roll bonded on the steel sheet. It was also shown that welding rotation and travel speed variation did not considerably impact the fracture loads in the... 

Al-1100/St-12 aluminum clad steel sheets were produced using roll bonding process at different reductions in thickness and with various supplemental annealing treatments. Experiments were conducted by applying the Taguchi method to obtain optimum condition for maximizing the joint strength. The joint strengths of the bi-layer sheets were evaluated by peel test. The Al/Fe intermetallic phases at the joint interface and the peeled surfaces were examined using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) and Vickers microhardness test were performed to characterize the intermetallic compounds. The results indicate that at the optimum condition of 0.50 reduction in... 

Copper-graphite composites which have low friction coefficient can be used as bearing materials in lieu of materials containing lead which cause environmental problems. So far, some methods such as powder metallurgy and centrifugal casting have been employed to produce these composites. In this study, friction stir processing (FSP) was used to produce copper-graphite surface composites. Five tools with different pin profile were employed in order to achieve a comprehensive dispersion. Results show that the tool with triangular pin gives rise to a better dispersion of graphite particles. Furthermore, four copper-graphite composites containing different graphite content were prepared using...