Sharif Digital Repository

The elastic behavior of an edge dislocation, which is positioned outside of a nanoscale elliptical inhomogeneity, is studied within the interface elasticity approach incorporating the elastic moduli and surface tension of the interface. The complex potential function method is used. The dislocation stress field and the image force acting on the dislocation are found and analyzed in detail. The difference between the solutions obtained within the classical-elasticity and interface-elasticity approaches is discussed. It is shown that for the stress field, this difference can be significant in those points of the inhomogeneity-matrix interface, where the radius of curvature is smaller and which... 

In this study, the effects of CeO2 nanoparticle addition on tensile strength and formation of interfacial intermetallic compound layer for lead-free Sn-3.5Ag-0.7Cu solder joint were investigated. The results showed that the thickness of intermetallic layer was decreased with increasing weight percentages of CeO2 reinforcements, and the growth of the intermetallic layer was remarkably suppressed during isothermal aging at 150 C. It was also found that the tensile strength of the solder joint gradually increased with the addition of CeO2 particles, reached to the maximum value at 0.5 wt% CeO2 and then decreased drastically with further increase in CeO2 content. Microstructural investigation of... 

Carbon-based perovskite solar cells (C-PSCs) have been considered to be promising candidates towards commercialization, due to their relatively low-production cost and excellent stability. However, the defects of the perovskite film and the mismatched energy level arrangement between perovskite layer and the carbon electrode (CE) severely limit the power conversion efficiency (PCE) of C-PSCs. Here, we incorporated pure-phase two-dimensional (2D) perovskite crystal (OA)2PbI4 (OA=n-octylammonium) as a passivation layer atop of 3D perovskite layer in C-PSCs. The modified films show significantly reduced defect state density, optimized energy level arrangement, and enhanced hydrophobicity. As a... 

Rockfall is a significant hazard to sites that are located at the foot of rock slopes. In such sites, there is a notable need to evaluate the potential for rockfall, estimate the extent of areas at risk, and design retaining structures to reduce the risk of rockfall-induced. This paper presents a probabilistic framework for predicting the formation and progression of rockfalls and for evaluating the performance of retaining walls under rockfalls. To this end, first a probabilistic model for the rock projectile motion on a slope is presented. The model accounts for prevailing uncertainties, i.e., the trigger points, rock shape, projectile path, and slope material properties, which include... 

As one of the key technologies for high performance electronic devices, composite solders have been recently developed to improve thermal and mechanical properties of solder joints. In this study, accumulative roll bonding process was used as an effective alternative method for manufacturing high-strength, finely dispersed, void-free and highly uniform Sn-Ag-Cu/CeO 2 nanocomposite solders. Microstructural investigation of nanocomposite solders revealed that homogenous distribution of CeO 2 nanoparticle has been achieved and the eutectic as-cast morphology of the solder changed to recrystallized fine grained structure. As a result of severe plastic deformation during rolling, brittle and... 

Zeolitic imidazole frameworks (ZIFs) provide an exciting platform to design and fabricate non-precious-metal carbon-based catalysts for oxygen reduction/evolution reaction (ORR/OER). Herein, we elaborately design a facile enzyme-assisted synthetic strategy that enables to tailor the ZIFs precursors into structural stable decussation shape, which derived Co nanoislands grafted on decussate N-doped carbon nanoleaves (D-Co@NC) can well retain the interpenetrating nanostructure. Benefiting from the combined advantages of compositions and interpenetrating nanostructures, D-Co@NC possesses 5.2 times higher exposed electrochemical active area than the conventional dodecahedral one, thus endowing... 

We study the asymmetric primordial fluctuations in a model of inflation in which translational invariance is broken by a domain wall. We calculate the corrections to the power spectrum of curvature perturbations; they are anisotropic and contain dipole, quadrupole, and higher multipoles with non-trivial scale-dependent amplitudes. Inspired by observations of these multipole asymmetries in terms of two-point correlations and variance in real space, we demonstrate that this model can explain the observed anomalous power asymmetry of the cosmic microwave background (CMB) sky, including its characteristic feature that the dipole dominates over higher multipoles. We test the viability of the... 

This paper presents a novel flexible control strategy for Unified Power Quality Conditioner (UPQC), which achieves more flexibility in compensation of power quality disturbances as compared to the existing methods. The proposed control strategy provides priority-based compensation as well as full and standard-based compensation considering the rating of series and shunt parts of a UPQC. The priority-based compensation is done based on the compensation priority among different power quality disturbances. In this control strategy, an on-line estimation of different voltage and current disturbances is required. For this purpose, a Unified Adaptive Power Quality Estimator (UAPQE) has been... 

Deployment of low-power low-cost small access points such as femtocell access points (FAPs) constitute an attractive solution for improving the existing macrocell access points' (MAPs) capacity, reliability, and coverage. However, FAP deployment faces challenging problems such as interference management and the lack of flexible frameworks for deploying the FAPs by the service providers (SPs). In this paper, we propose a novel solution that jointly associates the user equipment (UE) to the APs, and allocates the FAPs to the SPs such that the the total satisfaction of the UEs in an uplink OFDMA network is maximized. We model the competitive behaviors among the UEs, FAPs, and SPs as a dynamic... 

Consideration is given to shear-rate-dependent rheology effects on mass transport in a heterogeneous microreactor of rectangular cross section, utilizing both numerical and analytical approaches. The carrier liquid obeys the power-law viscosity model and is actuated primarily by an electrokinetic pumping mechanism. It is discovered that, considering the shear-thinning biofluids to be Newtonian fluids gives rise to an overestimation of the saturation time. The degree of overestimation is higher in the presence of large Damkohler numbers and electric double layer thicknesses. It is also increased by the application of a favorable pressure gradient, whereas the opposite is true when an opposed... 

In this paper, a modified partial derivative method is developed to predict the linear and nonlinear dynamic coefficients of tilting-pad journal bearings with journal and pad perturbation. To this end, Reynolds equation and its boundary conditions along with equilibrium equations of the pad are used. Finite difference, partial derivative method, and perturbation technique have been employed simultaneously for solving these equations. The accuracy of the results is investigated by comparing the linear dynamic coefficients of three types of tilting-pad journal bearings with those published the literature. It is shown that the nonlinear dynamic coefficients depend on Sommerfeld number,... 

Amorphous chalcogenides in the form of bulk or thin films are known as photosensitive materials that undergo changes in optical or structural properties upon irradiation. Here we study the optical properties of nanocomposite films of ZnS-SiO2 illuminated with ultraviolet (UV) light and relate them to the photo-induced evolution of roughness, as well as photo-crystallization effects in these films. We observe that upon UV irradiation a new crystalline phase of ZnSiO3 is formed in the nanocomposite film. This is accompanied by the evolution of surface roughness on the film. © 2005 IOP Publishing Ltd  

Motivated by the puzzling optical conductivity measurements in graphene, we speculate on the possible role of strong electronic correlations on the two-dimensional Dirac fermions. In this work we employ the slave-particle method to study the excitations of the Hubbard model on honeycomb lattice, away from half-filling. Since the ratio U/t ≈ 3.3 in graphene is not infinite, double occupancy is not entirely prohibited and hence a finite density of doublonscan be generated. We therefore extend the Ioff-Larkin composition rule to include a finite density of doublons. We then investigate the role played by each of these auxiliary particles in the optical absorption of strongly correlated Dirac... 

While standard Empirical Risk Minimization (ERM) training is proven effective for image classification on in-distribution data, it fails to perform well on out-of-distribution samples. One of the main sources of distribution shift for image classification is the compositional nature of images. Specifically, in addition to the main object or component(s) determining the label, some other image components usually exist, which may lead to the shift of input distribution between train and test environments. More importantly, these components may have spurious corre-lations with the label. To address this issue, we propose Decompose-and-Compose (DaC), which improves robustness to correlation... 

In this study, based on the reduced form of elasticity displacement field for a long laminate, an analytical method is established to exactly obtain the interlaminar stresses near the free edges of generally laminated composite plates subjects to extension, torsion, and bending. The constant parameters being in the displacement field, which describe the global deformation of a laminate, are appropriately calculated by using the improved first-order shear deformation theory. Reddy's layerwise theory is subsequently employed for analytical and numerical examinations of the boundary layer stresses within arbitrary laminated composite plates. Various numerical results are developed for the... 

The 3A zeolite is an excellent adsorbent for natural gas dehydration due to low energy requirement in regeneration step and easy operation. To perform a reliable modeling, a good equilibrium adsorption isotherm is mandatory. Accordingly, water, methane, methyl mercaptan (M-mercaptan) and CO2 adsorption isotherms and also the competitive adsorption loading versus temperature are described for the system using molecular simulation and mathematical models. It is found that CO2 competes with water for adsorption on 3A and lower temperature is required for selective removal of water. The mathematical model results showed that M-mercaptan and CO2 quickly adsorb on 3A and capacity of 3A for water... 

Energy Return on Investment (EROI) is an indicator of how efficient is an energy supply system. In the present study, the conventional approach of EROI assessment is extended to include the equivalent energy investment needed for offsetting the life cycle environmental impacts. Moreover, the issue of allocation of the invested energy among different by-products is addressed. The EROI of multiple products has been specified using different benchmarks of price, energy content, exergy content, and exergy costs. The application of the concept is demonstrated through a case study of an Iranian oil production unit. The overall conventional and environmentally-extended EROI values of the produced... 

The present study compared different approaches to assessing the environmental cost-effectiveness of energy policy scenarios. As a case study, the megacity of Tehran in Iran was studied. A key policy challenge in this city is to curb high concentrations of PM2.5 and mitigate the associated adverse impacts. The results demonstrated that in the business as usual case, the spatially averaged primary and secondary PM2.5 concentration in Tehran will increase by 30% in the 2010–2030 period. Adopting certain planned policy scenarios and the corresponding pollutant concentration reductions in Tehran shows that although most of the emission comes from industrial activities around the city, the... 

High-density, ultrasmall-pitch electronic applications require miniaturized solder bumps with improved thermomechanical performance. In addition, novel techniques which are able to precisely characterize these solder bumps are needed. One approach to meeting both of these requirements is to make use of recently developed nanocomposite solders with enhanced creep resistance, and to characterize these solders using a nanoindentation technique. In the present study, the creep behavior of ceria-reinforced nanocomposite solder foils fabricated by the accumulative roll-bonding process was characterized using a depth-sensing nanoindentation technique. It was found that the creep resistance of the... 

In this paper, a combined model of auto-transit assignment is introduced based on two complementarity formulations in the literature. The model accounts for interactions between the auto and transit modes through non-separable asymmetric demand and cost functions. A path-based solution algorithm is presented based on the three ideas of decomposition, column generation, and linearization, which have proved to be effective in tackling large-size networks. Numerical results over the Chicago sketch network suggest that the algorithm converges quickly within the first iterations, but is less effective as the solution gets closer to the neighborhood of the equilibrium solution. The sluggish...