Sharif Digital Repository

Aluminum use for automotive body sheet applications is growing. This growth requires improvement of related joining processes and technologies. Resistance spot welding will be one of the major joining technologies used in assembling automobiles. In this study the effects of weld current and time on the spot weldability of aluminum alloy 5754 autobody sheet were investigated. The results indicate that the influence of weld current on spot weldability of aluminum is more significant comparing to the weld time. The results also show that the weld current within 15-22 kA is more significant than 22-30 kA range of weld current. There is a linear relation between shear strength and nugget... 

The electrodeposition of binary Ni-Fe alloys is studied in chloride-based solutions with organic additives. Specific codeposition composition of the electrolyte and operating variables are taken for deposition a wide range of Ni-Fe deposits. Results reveal that in solutions containing sodium citrate and glycolic acid, the nickel content always increases with the current density and nickel concentration. Therefore, nickel reduction rate and the Ni/Fe ratio in the deposits increase. The anomalous codeposition of iron is minimized and the quality of the alloy deposits is improved with the combination of sodium citrate and glycolic acid. Scanning electron micrographs show that, with addition of... 

In This paper detailed frequency-domain system identification method is applied to identify steering dynamics of a naval coastal patrol vessel using a data analysis software tool, called CIFER. Advanced features such as Chirp-Z transform and composite windowing techniques are used to extract high quality frequency responses. An accurate, linear and robust transfer function models are derived for yaw and roll dynamics of the vessel. In addition, to evaluate the accuracy of the identified model, time-domain responses from a 45-45 zig-zag test are compared with the responses predicted by the identified model. The model shows excellent predictive capability that is well suited for simulation... 

The Zagreb indices have been introduced by Gutman and Trinajstić as M1(G) = ∑ v∈V (G) (dG(v))2 and M2(G) = ∑ uv∈E(G) dG(u)dG(v), where dG(u) denotes the degree of vertex u. We now define a new version of Zagreb indices as M1 *(G) = ∑ uv∈E(G) [εG(u) + εG(v)] and M2 * (G) = ∑ uv∈E(G) εG(u)εG(v), where εG(u) is the largest distance between u and any other vertex v of G. The goal of this paper is to further the study of these new topological index  

Omega polynomial was introduced by Diudea. Following Omega polynomial, the Sadhana polynomial was defined by Ashrafi et al. In this paper we compute Omega and Sadhana polynomials of three classes of dendrimers  

The ABC index is a topological index was defined as where dG(u) denotes degree of vertex u. Now we define a new version of ABC index as where The goal of this paper is further the study of the ABC4 index  

Let ∑ be the class of finite graphs. A topological index is a function Top from ∑ into real numbers with this property that Top(G) = Top(H), if G and H are isomorphic. is defined as half sum of the distances between all the pairs of vertices in a molecular graph. The goal of this paper is to further the study of Wiener index of special case of a chain of fullerenes  

The Zagreb indices have been introduced more than thirty years ago by Gutman and Trinajstić. In this paper we introduce a new version of Zagreb indices and then we compute them for an infinite family of nanostar dendrimers  

This paper presents nonlinear signal and noise analysis of a wide gate FET mixer. The study is performed using nonlinear sliced modeling. The FET is taken into account as a distributed element and divided into several smaller pieces so that in each slice a lumped model can be applied. Calculation of passive and active elements of each slice is performed using proper scaling approach. For noise analysis, appropriate noise sources are added to the distributed circuit The wide gate FETs have been suggested for high power, wideband and high gain devices such as travelling wave amplifier. The nonlinear application is suggested for a novel device named travelling wave mixer. © 2000 IEEE  

The influence of the loading of the FET electrodes, on signal and noise performances of the device in mixer application is studied. It is shown that exciting the input signal from one end of the gate and extracting the output signal from the opposite ends of the gate can improve the device characteristics, provided that the two remaining ends of the gate and the drain are properly loaded. This structure makes the lines (i.e. the gate and the drain electrodes) to be matched with the loads. Therefore it leads to a travelling wave FET mixer, which is a good candidate for high power mm-wave application. © 2000 IEEE  

The knowledge of the conductivity across the reservoir that is based on the swept fraction controls the recoverable rates of the hydrocarbon in the secondary displacement processes. Most of the time, we need a fast estimation of the conductivity for decision making during field development. Percolation theory is a very useful tool to get this goal. According to this fact that the results of this method are universal, they could be used widely. In this study connectivity and conductivity percolation models are developed and the universal exponents for connectivity and conductivity in fractured reservoir as well as their dependency on the correlation length are investigated. For L< ξ the... 

Carbon nanotubes were electrodeposited in acetonitrile solution at room temperature using Cu, and Fe-Ni nanoparticles as nucleation sites on HF-etched Si(100) wafer substrate. The electrochemical behavior of the deposition was investigated by voltammetry and chronoamperometry techniques. In order to obtain the optimum growth condition, the deposition critical parameters including current density range, potential and time were studied and calculated. Carbon nanotubes with approximate external diameter of 40-100 nm were fabricated under potentiostatic condition and diffusion control at - 20 V in 4-6 h. The film crystallinity was investigated by means of X-ray diffraction and the tubes... 

Electrodeposition of gold nanowires is carried out in cyanide solution in polycarbonate templates with pore diameter of 80 nm. Electrochemical methods are utilized to characterize the gold electrodeposition and to obtain the nucleation and growth mechanism. The analysis of cyclic voltammograms shows that the electrodeposition of gold nanowires takes place under diffusion control. Current transients reveal that nucleation mechanism is instantaneous with a three-dimensional growth process. The transition-time measurements show that the gold elecrodeposition occurs as one-electron valence involved in the reaction mechanism. Charge transfer coefficient is also found to be 0.67 ± 0.01. The value... 

The electrocodeposition of Ni-TiO2 nanocomposite single layers and Ni-TiO2/TiO2 multilayers from a Watts bath containing a TiO2 sol on copper substrates was investigated by different deposition techniques. Compared with direct current (DC) deposition, both pulse plating (PP) and pulse reverse plating (PRP) facilitated higher incorporations of TiO2 nanoparticles. Morphological studies conducted by scanning electron microscopy and field emission scanning electron microscopy revealed that the microstructure of the Ni-TiO2 nanocomposite coatings are affected both by pulse potentials and durations, indicating that higher incorporations of TiO2 nanoparticles refine the microstructure. The results... 

The knowledge of the conductivity across the reservoir that is based on the swept fraction controls the recoverable rates of the hydrocarbon in the secondary displacement processes. Most of the time, we need a fast estimation of the conductivity for decision making during field development. Percolation theory is a very useful tool to get this goal. According to this fact that the results of this method are universal, they could be used widely. In this study connectivity and conductivity percolation models are developed and the universal exponents for connectivity and conductivity in fractured reservoir as well as their dependency on the correlation length are investigated. For L< ξ the... 

The knowledge of the connectivity across the reservoir not only helps to find out the potential oil recovery within a particular well configuration but also affects on the other reservoir engineering decisions such as infill drilling. Connectivity also controls the swept fraction of the hydrocarbon in place in secondary displacement other than the recoverable rates of the hydrocarbon. Most of the time we need a fast estimation of connectivity for decision making during field development. Percolation theory is a very useful tool to get this goal. According to this fact that the results of this method are universal, they could be used widely. During this study a percolation model is developed... 

Reaction thrusters (RTs) are used as an alternative to momentum exchange devices when disturbance torques exceed the control authority of momentum exchange devices. The reaction control system (RCS) can employ some rocket thrusters to provide attitude control during the thrusting or coast phase. Within the control loop, the RCS's target could be either achieving and keeping a certain attitude or controlling the rate of an attitude change. In the coast phase, some tasks such as preacceleration, settling of liquid propellant, damping of structural vibrations, providing a velocity increment to separate stages and payloads, and carrying out orbital and nonorbital maneuvers may be included in its... 

The sol-enhanced pulse plating (PP) technique was utilized to deposit the Ni-TiO2/TiO2 multilayers on copper substrates from a Watts bath containing a TiO2 sol, and the obtained coatings were heat treated at various temperatures. The characteristics of coatings were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and UV-visible spectrophotometry. In order to estimate the wettability of these nanostructured multilayers after exposure to UV light, the contact angle of water droplets were measured, and the photocatalytic (PC) efficiency of the multilayers were analyzed by the degradation of methyl... 

The wear and friction properties of G-Cu (Sn) composite coatings containing different amounts of graphite particles were examined. The presence of graphite particles improved antifriction properties of composite coatings. The effects of graphite percent in composite coating, tin content of matrix, load, speed and distance on the coefficient of friction and wear resistance of bronze-graphite composite coatings were studied. The results of the present studies revealed that hardness, wear resistance, coefficient of friction are dependent on volume percentage of graphite in composite coating. It was shown that the composite coating containing approximately 5.4 (vol.%) graphite and matrix with... 

The spin and orbital angular momentum of photons can perturb during propagation in few mode optical fiber, and hence, in the receiver, perturbations must be adjusted. For polarization adjustment, polarization controllers have been developed previously. In this paper, we show that in the presence of external effects such as tension and tortion, the entanglement between the different degrees of freedom of a photon does not change. A device for simultaneous adjustment of polarization and spatial distribution in few mode fiber is proposed. In addition to modification, this device can also be used to produce different modes in fiber. © 2023 Optica Publishing Group under the terms of the Optica...