Sharif Digital Repository

Recently, some works have been done in studying activity network as a more realistic representation of users’ behavior in online social networks. However, there is a major deficiency of a suitable definition of activity network based on a comprehensive study of various activity networks separately and combined. The main purpose of our research is to understand the differences between users’ behavior by various Facebook activities, so as to claim that these networks should not be blindly composed; neither should the result of analyzing each of them individually be generalized to others. For this purpose, degree distribution, small-world phenomenon, degree correlation, reciprocity, and... 

Recently, some works have been done in studying activity network as a more realistic representation of users’ behavior in online social networks. However, there is a major deficiency of a suitable definition of activity network based on a comprehensive study of various activity networks separately and combined. The main purpose of our research is to understand the differences between users’ behavior by various Facebook activities, so as to claim that these networks should not be blindly composed; neither should the result of analyzing each of them individually be generalized to others. For this purpose, degree distribution, small-world phenomenon, degree correlation, reciprocity, and... 

Traditional fragmented and mechanistic science is unable to cope with issues about sustainability, as these are often related to complex, self-organizing systems. In the paper, sustainable development is seen as an unending process defined neither by fixed goals nor by specific means of achieving them. It is argued that, in order to understand the sources of and the solutions to modern problems, linear and mechanistic thinking must give way to non-linear and organic thinking, more commonly referred to as systems thinking. System Dynamics, which operates in a whole-system fashion, is put forward as a powerful methodology to deal with issues of sustainability. Examples of successful... 

We propose an effective medium theory for a one-dimensional periodic array of rectangular grooves covered by a graphene sheet. Parameters of the effective medium model are given by explicit analytical expressions for both major polarizations TM and TE, and for all incident angles. In extraction of this model, we assumed single mode approximation inside the grooves. The effect of non-specular diffraction orders outside the grating, as well as the plasmonic response of the graphene sheet in the far-infrared spectrum, is addressed by introducing an effective surface conductivity at the interface of the metallic grating and the ambient environment. It is shown that surface plasmons in graphene... 

1-D compound metallic grating (CMG) is a periodic structure with more than one slit in each period. When CMG is combined with a graphene sheet as its cover, the incident light is effectively coupled to the plasmons in graphene which in turn can result in strong manipulation of light for both major polarizations. We show that tunable phase resonance and perfect absorption of the incident light are interesting outcomes of this manipulation. In this paper, we demonstrate that fano-like phase resonances which can be observed in CMGs under transverse magnetic polarized incident wave are tuned by changing the Fermi level of graphene. It is shown that while the spectral position of the phase... 

The groundwater system in the Rafsanjan aquifer perpetuated sustainably for decades before 1950s; however, its groundwater resources have been overexploited in the recent decades. In this paper, we aim to investigate the water governance system to understand the reasons behind the ongoing overexploitation. Sustainability processes are considered a policy implementation problematic. As such, we employ the contextual interaction theory as a policy implementation framework to assess the groundwater governance as part of the context for the conservation policy. Data for this qualitative research were gathered from legal texts, articles, technical reports, and multiple interviews with authorities... 

We show that a metal-organic framework (MOF) sustained by a nanosized Ag12 cuboctahedral node can be applied to selectively extract traces of lead(II) ion from environmental water samples. The MOF was characterized by thermogravimetric and differential thermal analysis, scanning electron microscopy, FTIR, and X-ray diffraction. The effects of pH value, flow rates, of type, concentration and volume of the eluent, of break-through volume and potentially interfering ions on the separation and determination of lead were evaluated. Following desorption with EDTA, Pb(II) was quantified by FAAS. The use of the MOF results in excellent analytical figures of merit including an analytical range from 2... 

We show that a plasmonic semiconductor substrate can support highly confined surface plasmons when it is covered by a graphene layer. This occurs when the imaginary part of graphene conductivity and real part of the effective permittivity of the surrounding medium become simultaneously negative. Full-wave electromagnetic simulations demonstrate the occurrence of negative refraction and two-dimensional lensing at the interface separating regions supporting conventional right-handed graphene plasmons and left-handed surface plasmon polaritons. © 2018 Optical Society of America  

A new gelator based of oleylamide has been introduced, which was gelled nonpolar hydrocarbon and CCl4 solvents through self-assembly. Also, the gelator formed a two-component hydrogel in combination with SDS, an anionic surfactant. UV-Vis studies revealed that the H-type and J-type aggregation of organogels in hexane and hydrogel in water, respectively. The xerogel, obtained by evaporating the solvent of organogel, selectively gelled and adsorbed oil spills on water surfaces. The effect of the various parameters, including temperature, water acidity and pH on the oil spill adsorption was studied, revealing the high ability of the xerogel to removing the oil contamination from water in up to... 

An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading  

In CW forward scatter radars, Space-Time processing by 2-D FFT is used to estimate Doppler frequency shift and angle of arrival concurrently. 2-D periodogram and 2-D Capon methods are two famous spectral estimation methods which can be substituted for 2-D FFT. Here we will provide analysis of performance for these methods beside their cons and pros