Showing papers by "Iran University of Science and Technology published in 2008"

Utilization of copper slag in cement and concrete

Abstract: Copper slag is a by-product obtained during matte smelting and refining of copper. The common management options for copper slag are recycling, recovering of metal, production of value added products such as abrasive tools, roofing granules, cutting tools, abrasive, tiles, glass, road-base construction, railroad ballast, asphalt pavements. Despite increasing rate of reusing copper slag, the huge amount of its annual production is disposed in dumps or stockpiles to date. One of the greatest potential applications for reusing copper slag is in cement and concrete production. Many researchers have investigated the use of copper slag in the production of cement, mortar and concrete as raw materials for clinker, cement replacement, coarse and fine aggregates. The use of copper slag in cement and concrete provides potential environmental as well as economic benefits for all related industries, particularly in areas where a considerable amount of copper slag is produced. This paper reviews the characteristics of copper slag and its effects on the engineering properties of cement, mortars and concrete.

Analytical Model for Connectivity in Vehicular Ad Hoc Networks

Abstract: We investigate connectivity in the ad hoc network formed between vehicles that move on a typical highway. We use a common model in vehicular traffic theory in which a fixed point on the highway sees cars passing it that are separated by times with an exponentially distributed duration. We obtain the distribution of the distances between the cars, which allows us to use techniques from queuing theory to study connectivity. We obtain the Laplace transform of the probability distribution of the connectivity distance, explicit expressions for the expected connectivity distance, and the probability distribution and expectation of the number of cars in a platoon. Then, we conduct extensive simulation studies to evaluate the obtained results. The analytical model that we present is able to describe the effects of various system parameters, including road traffic parameters (i.e., speed distribution and traffic flow) and the transmission range of vehicles, on the connectivity. To more precisely study the effect of speed on connectivity, we provide bounds obtained using stochastic ordering techniques. Our approach is based on the work of Miorandi and Altman, which transformed the problem of connectivity distance distribution into that of the distribution of the busy period of an equivalent infinite server queue. We use our analytical results, along with common road traffic statistical data, to understand connectivity in vehicular ad hoc networks.

Phase-Shifted Carrier PWM Technique for General Cascaded Inverters

Abstract: Phase-shifted carrier (PSC) pulsewidth modulation (PWM) in its conventional form is a good solution for single-phase Cascaded inverters as alternative phase opposition disposition (APOD) PWM for single-phase diode clamped inverters. PSC distributes the switching angles of APOD PWM waveform among the legs uniformly and reduces the switching frequency of each leg. This paper proposes a modified PSC technique based on partly shifted carriers for all disposition types including phase disposition (PD) which is suitable for three-phase cascaded inverters. Simulation results are also included for using carrier-based space-vector PWM (SVPWM).

Effects of silica fume addition and water to cement ratio on the properties of high-strength concrete after exposure to high temperatures

Abstract: This paper presents the results of an experimental investigation on the effect of different amounts of silica fume (SF) and water to cement ratios (w/c) on the residual compressive strength of high-strength concrete after exposure to high temperatures. Based on the results obtained the rates of strength loss for concrete specimens containing 6% and 10% SF at 600 °C were 6.7% and 14.1% lower than those of the ordinary concrete. The dosage of SF had no significant effect on the relative residual compressive strength at 100 and 200 °C, whereas the amount of SF had considerable influences on the residual compressive strength above 300 °C similar to the response at 600 °C. The optimum dosage of SF and w/c was found to be 6% and 0.35, respectively.

CO2 reforming of CH4 over nanocrystalline zirconia-supported nickel catalysts

Abstract: Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174 m2 g−1 after calcination at 700 °C for 4 h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50 h of reaction. Addition of promoters (CeO2, La2O3 and K2O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50 h of reaction.

Microstructure and failure behavior of dissimilar resistance spot welds between low carbon galvanized and austenitic stainless steels

Abstract: Resistance spot welding was used to join austenitic stainless steel and galvanized low carbon steel. The relationship between failure mode and weld fusion zone characteristics (size and microstructure) was studied. It was found that spot weld strength in the pullout failure mode is controlled by the strength and fusion zone size of the galvanized steel side. The hardness of the fusion zone which is governed by the dilution between two base metals, and fusion zone size of galvanized carbon steel side are dominant factors in determining the failure mode.

Densification and grain growth of nanocrystalline 3Y-TZP during two-step sintering

Abstract: Two-step sintering (TSS) was applied on nanocrystalline yttria tetragonal stabilized zirconia (3Y-TZP) to control the grain growth during the final stage of sintering. The process involves firing at a high temperature (T1) followed by rapid cooling to a lower temperature (T2) and soaking for a prolonged time (t). It is shown that for nanocrystalline 3Y-TZP (27 nm) the optimum processing condition is T1 = 1300 °C, T2 = 1150 °C and t = 30 h. Firing at T1 for 1 min yields 0.83 fractional density and renders pores unstable, leading to further densification at the lower temperature (T2) without remarkable grain growth. Consequently, full density zirconia ceramic with an average grain size of 110 nm is obtained. XRD analysis indicated that the ceramic is fully stabilized. Single-step sintering of the ceramic compact yields grain size of 275 nm with approximately 3 wt.% monoclinic phase. This observation indicates that at a critical grain size lower than 275 nm, phase stabilization is induced by the ultrafine grain structure.

Molecular interactions of cationic and anionic surfactants in mixed monolayers and aggregates.

Abstract: The properties of anionic-rich and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry and surface tension measurements and by determining the surfactant NMR self-diffusion coefficients. The critical aggregate concentration (CAC), surface tension reduction effectiveness(γCAC), surface excess(Γmax), and mean molecular surface area (Amin) were determined from plots of the surface tension (γ) as a function of the total surfactant concentration. The compositions of the adsorbed films (Z) and aggregates (χ) were estimated by using regular solution theory, and then the interaction parameters in the aggregates (β) and the adsorbed film phases (βσ) were calculated. The results showed that the synergism between the surfactants enhances the formation of mixed aggregates and reduces the surface tension. Further, the nature and strength of the interaction between the surfactants in the mixtures were obtained by calculating the values of...

Phase I Monitoring of Polynomial Profiles

Abstract: In some statistical process control applications, quality of a process or product is characterized by a relationship between two or more variables which is referred to as profile. In many practical situations, a profile can be modeled as a polynomial regression. In this article, three methods are developed for monitoring polynomial profiles in Phase I. Their performance is evaluated using power criterion. Furthermore, a method based on likelihood ratio test is developed to identify the location of shifts. Numerical simulation is used to evaluate the performance of the developed method.

Optimal Design of Transmission Towers Using Genetic Algorithm and Neural Networks

Abstract: In the context of transmission tower optimization, the energy method and the force method are combined in order to form a holistic design and optimization approach, eliminating the need for time-intensive matrix inversion. A migration genetic algorithm is employed in the optimization process. Although this algorithm is suitable for towers with a limited number of elements, it is inefficient in the case of many towers encountered in practice. The addition of a neural network as an analysis tool reduces the overall computational load. Four examples are presented to demonstrate the important role of neural networks in reducing the computational overhead.

Enhancing AODV routing protocol using mobility parameters in VANET

Abstract: VANET is new generation of ad hoc networks that implement between vehicles on a road. Because of high mobility, routing in VANET has more problems than MANET. Thereby, in this paper we propose a modification on AODV as MANET routing protocol to make it adaptive for VANET. When a node is mobile, it has three mobility parameters: position, direction and speed. In our method, we have used direction as most important parameter to select next hop during a route discovery phase. With respect to mobility model, if nodes has same direction with source and/or destination nodes, our solution might selects them as a next hop. Position is another parameter that we used for next hop selection.

Integrating system dynamics and fuzzy logic modelling for construction risk management

Abstract: The complex structure of construction project risks arises from their internal and external interactions with their dynamic nature throughout the life cycle of the project. A system dynamics (SD) approach to construction project risk management is presented, including risk analysis and response process. Owing to the imprecise and uncertain nature of risks, fuzzy logic is integrated into system dynamics modelling structure. Risk magnitudes are defined by a fuzzy logic based risk magnitude prediction system. Zadeh's extension principle and interval arithmetic is employed in the SD simulation model to present the system outcomes considering uncertainties in the magnitude of risks resulting from the risk magnitude prediction system. The performance of the proposed method is assessed by employing the method in the risk management plan of a sample project. The impact of a sample risk is quantified and efficiency of different alternative response scenarios is assessed. The proposed approach supports different st...