Sharif Digital Repository

Let (Formula presented.) be a graph of order (Formula presented.) and size (Formula presented.). Suppose that (Formula presented.) is a function such that (Formula presented.). In this paper we provide a criterion for (Formula presented.)-choosability of (Formula presented.). Using this criterion, it is shown that the choice number of the complete (Formula presented.)-partite graph (Formula presented.) is (Formula presented.), which is a well-known result due to Erdös, Rubin and Taylor. Among other results we study the (Formula presented.)-choosability of the complete (Formula presented.)-partite graphs with part sizes at most (Formula presented.), when (Formula presented.), for every vertex... 

TiO2 nanorods have been successfully grown into a track-etched polycarbonate (PC) membrane by a particulate sol-electrophoretic deposition from an aqueous medium. The prepared sols had a narrow particle size distribution around 17 nm and excellent stability against aging, with zeta potentials in the range of 47-50 mV at pH 2. It was found that TiO2 nanorods were grown from dilute aqueous sol with a low, 0.1-M concentration. Fourier transform infrared spectroscopy (FT-IR) analysis confirmed that a full conversion of titanium isopropoxide was obtained by hydrolysis, resulting in the formation of TiO2 particles. X-ray diffraction (XRD) results revealed that TiO2 nanorods dried at 100 °C were a... 

The expected lifetime of a power electronic converter is limited by its fragile components such as semiconductor devices and capacitors. These components are prone to wear-out failures depending on the converter mission profile and component thermal characteristics. This paper explores the wear-out failure of the power converter semiconductor devices in inverting and rectifying modes of the converter using different power factors. The obtained results show the different wear-out characteristics of a converter under rectification, inversion, and also partial-inversion/rectification modes as well as when provides reactive power support. Moreover, this paper proposes B10 lifetime curves to... 

Frequency estimation of vapor cloud explosions (VCE) are traditionally based on sparse VCE incidents data analysis while process conditions that generate VCE's have a wide spectrum giving VCE's with different strengths. The present paper is focused on developing a systematic methodology to estimate the frequency of VCEs based on process and plant conditions in order to find optimal location of a control room using quantitative risk assessment (QRA). In the presented approach, after classification of plant areas according to variables likely to generate different release conditions, a comprehensive release study is carried out to determine individual probable leakages. Consequently, only... 

Safety distance has already been a main easurement for the hazard control of chemical installations interpreted to mean providing space between the hazardous installation and different types of targets. But, the problem is how to determine the enough space. This study considers the application of quantitative risk assessment to evaluating a compressed natural gas station site and to identify nearby land use limitations. In such cases, the most important consideration is to assure that the proposed site would not be incompatible with existing land uses in the vicinity. This scope is possible by categorization of estimated levels of risk imposed by the proposed site. It means that an analysis... 

API Recommended Practice 752 is one of the most referenced practices for evaluating vapor cloud explosion (VCE) impacts to site occupied buildings. This reference introduces generic VCE frequencies for different types of process units that are based on VCE incidents database. Although these reported VCE frequencies are not capable of illustrating all parameters that affect explosion likelihood, they are widely used in risk analysis studies and software packages. This paper delineates the structure of a more realistic method for estimation of local VCE frequencies for independent congested spaces or units as a function of process, site, and meteorological variables. Compared to traditional... 

This study considers the application of quantitative risk assessment (QRA) on the siting of compressed natural gas (CNG) stations and determining nearby land use limitations. In such cases the most important consideration is to be assured that the proposed site would not be incompatible with existing land uses in the vicinity. It is possible by the categorization of the estimated levels of individual risk (IR) which the proposed site would impose upon them. An analysis of the consequences and likelihood of credible accident scenarios coupled with acceptable risk criteria is then undertaken. This enables the IR aspects of the proposed site to be considered at an early stage to allow prompt... 

The commuting graph of a ring R, denoted by Γ(R), is a graph of all whose vertices are noncentral elements of R, and 2 distinct vertices x and y are adjacent if and only if xy = yx. In this article we investigate some graph-theoretic properties of Γ (kG), where G is a finite group, k is a field, and 0 ≠ ⌊G⌋ j∈ k. Among other results it is shown that if G is a finite nonabelian group and k is an algebraically closed field, then GΓ (kG) is not connected if and only if ⌊G⌋ = 6 or 8. For an arbitrary field k, we prove that Γ (kG)is connected if G is a nonabelian finite simple group or G' ≠ G" and G"≠ 1  

Hydrophobic titania nanoparticles were synthesized by a novel in situ sol-gel method and applied in a single drop liquid-liquid extraction column to enhance the overall dispersed-phase mass transfer coefficient (Kod). The chemical system of toluene, acetic acid and water was used, and the direction of solute (acetic acid) mass transfer was from dispersed phase, including: toluene and acetic acid to the continuous phase of water. For such system, much of the mass transfer resistance exists in the dispersed phase, which is nonpolar organic liquid. Hence, modified titania nanoparticles (MTNP's), prepared by sol-gel route, in five different concentrations of 0.001–0.005 wt.% were added in the... 

The novel mixed ligand complexes [M(bpy)(phen-dione)](PF6)2 (M = Zn(II), Cd(II) and Hg(II), bpy = 2,2′-bipyridine and phen-dione = 1,10-phenanthroline-5,6-dione) have been synthesized and characterized by elemental analysis, IR, 1H NMR and electronic absorption spectroscopies. The ν(C=O) of coordinated phen-dione in these complexes are very similar to the free phen-dione ligand showing that phen-dione is not coordinated to metal ion from its C=O sites. Absorption spectra of the complexes show two absorption bands for intraligand transitions. These absorption bands show dependence to the dielectric constant of solvent. These complexes exhibit an intensive fluorescence band around 535 nm in... 

The mononuclear complexes of Zn(II), Cd(II) and Hg(II), [Zn(phen-dione)Cl2], [Cd(phen-dione)Cl2] and [Hg(phen-dione)Cl2], where phen-dione = 1,10-phenanthroline-5,6-dione, have been synthesized and characterized by elemental analysis and IR, 1H NMR and electronic absorption spectroscopies. The ν(C=O) of coordinated phen-dione ligands in these complexes shows that the phen-dione is not coordinated to metal ion from its C=O sites. Electronic spectra of the complexes show two absorption bands for intraligand transitions. These absorption bands show dependence on the dielectric constant of solvents. These complexes exhibit an intense fluorescence band around 545 nm in DMSO when the excitation... 

Elastic contact problem of a tilted shallow wedge with a half-plane is considered. The problem is solved analytically in either full slip or partial slip conditions. Closed-form expression is given for the Muskhelishvili's potential function of the contact. In the partial slip condition, the locations of the stick and slip zones were given explicitly in terms of the applied external loads and coefficient of friction. The results have been compared with finite elements modelling results. © 2007 Elsevier Ltd. All rights reserved  

In this paper, the elastic contact problem of an asymmetrical shallow wedge with a half-plane is considered. The potential function of the contact problem has been obtained through a simple approach. This approach simplifies the routine method of determination of potential functions in elastic contact problems. Then this approach was utilized to solve the aforementioned geometry under frictionless and frictional condition. Utilization of the new relation not only simplifies the procedure of solving contact problems but also is very helpful for fretting fatigue studies. © 2007 Elsevier Ltd. All rights reserved  

A special hybrid genetic algorithm (GA) is designed to solve the long-term coordination of hydro-thermal power systems with cascaded reservoirs and stochastic inflows. Since decision variables are continuous, in the proposed GA we employ real number rather than binary encoding. To create superior children we introduce dynamic tuning of the weights of operators. An exponential normalization is also developed such that better chromosomes have more chance to reproduce. To test the proposed method, 16 GAs are investigated which differ based on real or binary encoding, dynamic tuning or fixed weights for operators, inverse or exponential normalization and mixed or pure random initial populations.... 

In this paper, we propose an efficient method for demodulating pulse position modulation (PPM) signals based on Reed-Solomon decoding algorithm. It is shown that the proposed technique outperforms other demodulating methods such as those based on Lagrange, Spline, and Iterative algorithms. Furthermore, the proposed method is generalized to the case that the PPM signal is corrupted by additive white Gaussian noise. © 2004 Elsevier B.V. All rights reserved  

The steady 2-D boundary layer flow over a flat plate is studied analytically by homotopy perturbation method to analyze the entropy generation inside the boundary layer with constant wall temperature. By the transformations of go-verning equations including continuity, momentum, and energy by similarity va-riables, a dimensionless equation for entropy generation inside the boundary layer is obtained. The effects of important parameters such as Reynolds and Eck-ert numbers are investigated and the physical interpretations of the results are explained in details  

This study aimed to develop a drug carrier based on amine-functionalized mesoporous silica nanoparticles (AAS-MSNPs) for a poorly water-soluble drug, curcumin (CUR), and to study its effects on α-synuclein (α-Syn) fibrillation and cytotoxicity. Here, we show that AAS-MSNPs possess high values of loading efficiency and capacity (33.5% and 0.45 mg drug/mg MSNPs, respectively) for CUR. It is also revealed that α-Syn species interact strongly with the CUR-loaded AAS-MSNPs, leading to a significant inhibition of the fibrillation process. Furthermore, these samples reduce the toxic effects of CUR. However, drug-loaded AAS-MSNPs do not affect the cytotoxic properties of the formed fibrils... 

The effect of working fluid inventory and heat input on the performance of thermosyphon is investigated in this paper. First, a thermosyphon with diameter of 16 mm made of steel with toluene as working fluid and the length of the evaporator, adiabatic and condenser section 10, 23 and 17 cm was considered, respectively. The working fluid inventory was considered 0.1, 0.14, 0.18 and 0.24 of total volume of thermosyphon and in each case 54–235 W of heat input applied to the evaporator area also. In order to evaluate the transient behavior of the thermosyphon, in any amount of working fluid, 28 W of heat input was considered and temperature of the evaporator area were recorded at different... 

The effect of working fluid inventory and heat input on the performance of thermosyphon is investigated in this paper. First, a thermosyphon with diameter of 16 mm made of steel with toluene as working fluid and the length of the evaporator, adiabatic and condenser section 10, 23 and 17 cm was considered, respectively. The working fluid inventory was considered 0.1, 0.14, 0.18 and 0.24 of total volume of thermosyphon and in each case 54–235 W of heat input applied to the evaporator area also. In order to evaluate the transient behavior of the thermosyphon, in any amount of working fluid, 28 W of heat input was considered and temperature of the evaporator area were recorded at different... 

In this paper, an object oriented method is developed for generation, optimization and management of a hydrocarbon (CxHy) pyrolysis reaction network using a Bond-Electron (BE) matrix. A computer program was developed using C++ language. This program can provide and generate a pyrolysis reaction network for a wide range of hydrocarbons, including alkanes, olefins, diolefins, cyclic and aromatic compounds, using the linear notation structure of the reactant species. Furthermore, the reaction patterns and pruning methods are considered and a new method is presented for identification of reactants and products. The structural identification of species contained in the network allows one to...