Sharif Digital Repository

In this paper we consider the content distribution to a set of mobile users interested in the same content. We use the concept of mobile clouds, which exploits cooperation between mobile terminals over the low-power short-range links. We propose, formulate and investigate the energy efficiency and delay of four realistic cooperative content delivery strategies. The derived results, through analysis of mathematical models and simulations, demonstrate around 65% to 95% energy saving gain in mobile cloud strategies compared to conventional multicasting. We also show that using mobile clouds, content distribution delay can be reduced for up to 85%  

Baseboard heaters are a type of building heating systems that are placed along the base of the interior wall, instead of the traditional skirting. Baseboard heaters meet all the requirements of modern buildings such as thermal comfort, well-architected appearance, space-saving, efficient energy consumption, and fast thermal response. In the present study, we investigate the enhancement of the thermal output of hydronic baseboard heaters. For this purpose, several novel fin-tube arrays such as convector fins and fin-clips are proposed and the thermal performance of each array is evaluated experimentally. In addition, two different types of materials for the tubes, namely, copper and aluminum... 

Different models have been proposed for deposition of asphaltene on reservoir rocks that due to complexity of asphaltene nature, most of them have not been productive. Here, a reliable model is proposed which despite of previous models, considers the change in asphaltene saturation in the core. The obtained experimental data in the laboratory was used for model validation. In this work, a series of core flooding tests was carried out in presence of connate water at different solvent-oil volume ratios. Pressure drop was measured at three different terminals along the core. The obtained experimental data as well as mass balance equations, momentum equation, asphaltene deposition and... 

In this paper, we propose and study a context-aware leader selection algorithm within the concept of mobile clouds. We deploy a dedicated Cooperative Control Server (CCS) to assist and manage the process of leader selection more efficiently. The proposed algorithm collects data regarding instantaneous conditions of Mobile Terminals (MTs) and their radio environment; and then computes and assigns a rank to each MT. The ranks calculated based on a combination of different context-related parameters and corresponding weighting factors, allow selecting the leader. Furthermore, the energy efficiency and stability of the selected leaders is investigated for different parameter values through... 

We have designed and fabricated a dual-band circularly polarized antenna using a normally magnetized ferrite disk. The disk is metallized on top and is mounted on a grounded dielectric substrate. A hole is then punched at the center of the top metallization. The dual band operation of the antenna is due to two separate unidirectional resonances. The field intensity at the lower resonance is largest close to the outer periphery of the disk whereas at the higher resonance the electromagnetic field is concentrates near the punched hole. A two-section feeding network is used to feed the antenna. Central frequencies of the upper and lower bands are 4.62 GHz and 5.97 GHz, respectively.... 

Epoxy resins have been used as structural materials since the late 1940s. Despite their desirable properties such as high strength, excellent creep resistance, and good adhesion, they suffer from low fracture energy. Rubber modification as a major toughening approach to overcome the inherent brittleness of epoxy polymers was introduced during the early 1970s. Since then, a large number of investigations have been conducted to elucidate different aspects of rubber-toughened epoxies. The present work is a critical review of the field focusing on the important parameters affecting rubber-toughening. The studies reviewed are classified in five categories including roles of matrix ductility,... 

One of the biggest struggles while working with artificial neural networks is being able to come up with models which closely match biological observations. Biological neural networks seem to capable of creating and pruning dendritic spines, leading to synapses being changed, which results in higher learning capability. The latter forms the basis of the present study in which a new ionic model for reservoir-like networks, consisting of spiking neurons, is introduced. High plasticity of this model makes learning possible with a fewer number of neurons. In order to study the effect of the applied stimulus in an ionic liquid space through time, a diffusion operator is used which somehow... 

Multi-walled carbon nanotubes (MWCNTs) are one of the preferred candidates for reinforcing polymeric nanobiocomposites, such as acrylic bone type of cement. In this study, at first, bulk samples of the reinforced polymethylmethacrylate (PMMA) matrix were prepared with 0.1, 0.25, and 0.5 wt per wt% of MWCNTs by the casting method. Tensile and three-point bending tests were performed to determine the essential mechanical properties of bone cement, such as tensile and bending strengths. The tensile fracture surfaces were investigated by scanning electron microscopy (SEM). The commercial software (Abaqus) was used to conduct finite element analysis (FEA) by constructing a representative volume... 

In this paper, we study the problem of leader selection in the presence of selfish nodes in mobile ad-hoc networks (MANETs). In order to encourage selfish nodes to assume the leadership role, some form of incentive mechanism is required. We present an incentive-based leader selection mechanism in which incentives are incorporated in the form of credit transfer to the leader, which motivates nodes to compete with each other for assuming the leadership role. The competition among nodes is modeled as a series of one-on-one incomplete information, alternating offers bargaining games. Furthermore, we propose an efficient algorithm in order to reduce the communication overhead imposed on the... 

Crosstalk is the major limiting factor in DSL systems in terms of bit-rate or service coverage. Multiuser power control algorithms can be used to combat crosstalk degrading effects. The best ever known distributed power control solution is Iterative Water-filling (IWF). In this paper the performance of IWF in an ADSL system is considered in terms of offered rate-region and convergence speed. Then two novel modifications are proposed to accelerate convergence (usually 100-400%) without any performance loss. Therefore it suits better in practical applications, since each iteration needs re-initialization of the modem. © 2004IEEE  

Periodic metallic structures are known to support resonant extraordinary optical transmission (EOT). When covered with graphene, these structures can be employed to effectively manipulate the light. In this paper, we propose an analytical circuit model for graphene-covered 1-D metallic gratings. By using the circuit theory, we demonstrate that 1-D periodic array of cut-through slits, which are covered by a continuous graphene sheet, exhibits tunable EOT resonance for TM polarization whose amplitude, unlike its spectral position, can be dynamically tuned by varying the Fermi level of graphene. In this fashion, it is shown that placing a perfect reflector at the bottom of the graphene-covered... 

Free vibration response of a joined shell system including cylindrical and spherical shells is analyzed in this research. It is assumed that the system of joined shell is made from a functionally graded material (FGM). Properties of the shells are assumed to be graded through the thickness. Both shells are unified in thickness. To capture the effects of through-the-thickness shear deformations and rotary inertias, first-order shear deformation theory of shells is used. The Donnell type of kinematic assumptions is adopted to establish the general equations of motion and the associated boundary and continuity conditions with the aid of Hamilton’s principle. The resulting system of equations is... 

Free vibration response of a cylindrical shell closed with two hemispherical caps at the ends (hermit capsule) is analysed in this research. It is assumed that the system of joined shell is made from functionally graded materials (FGM). Properties of the shells are assumed to be graded through the thickness. Cylindrical and hemispherical shells are unified in thickness. To capture the effects of through-the-thickness shear deformations and rotary inertias, first order theory of shells is used. Donnell type of kinematic assumptions are adopted to establish the general equations of motion and the associated boundary and continuity conditions with the aid of Hamilton's principle. The resulting... 

Free vibration response of a cylindrical shell closed with two hemispherical caps at the ends (hermit capsule) is analysed in this research. It is assumed that the system of joined shell is made from functionally graded materials (FGM). Properties of the shells are assumed to be graded through the thickness. Cylindrical and hemispherical shells are unified in thickness. To capture the effects of through-the-thickness shear deformations and rotary inertias, first order theory of shells is used. Donnell type of kinematic assumptions are adopted to establish the general equations of motion and the associated boundary and continuity conditions with the aid of Hamilton's principle. The resulting... 

The objective of this study was to investigate the effects of two compatibilizers, namely maleated polypropylene (PP-g-MA) and maleic anhydride grafted poly (ethylene-co-octene) (EOC-g-MA), on the morphology and thus properties of ternary nanocomposites of polypropylene (PP)/ethylene-octene copolymer (EOC)/clay nanocomposite. In this regard the nanocomposites and their neat polymer blend counterparts were processed twice using a twin screw extruder. X-ray diffraction, transmission electron microscopy, Energy dispersive X-ray spectroscopy, and scanning electron microscopy were utilized to characterize nanostructure and microstructure besides mechanical and rheological behaviors of the... 

Organisational commitment is suggested as a remarkable variable in shaping employees’ attitudes toward knowledge management practices. Customer trust in services is established during a long-time relationship with a firm and improves the accuracy of information shared with employees. To put it in other words, customer trust is what a service company needs to maintain its competitive advantage. On the other hand, high employee turnover reflects a substantial loss of knowledge. In the present study, the impact of organisational commitment on employees’ retention, knowledge acquisition, and sharing was examined regarding the moderating roles of leader-member exchange and innovation climate. The... 

The effect of the nucleating agent masterbatch carrier resin on the nonisothermal crystallization of a pipe-grade polypropylene block copolymer was investigated at three different cooling rates using differential scanning calorimetry (DSC). Bis(3,4-dimethylibenzylidene) sorbitol (DMDBS), a well-known, third-generation sorbitol derivative, was used as a nucleating agent in this study. Crystallization kinetic parameters obtained from DSC cooling curves showed that incorporation of a nucleating agent by means of a masterbatch increased the crystallization rate by approximately two times compared to that of the sample with the same concentration of nucleating agent without the use of a... 

We experimentally demonstrate a circularly polarized antenna that utilizes unidirectional surface waves that propagate on the boundary of a small ferrite disk. The ferrite disk is metalized on top and is mounted on a grounded dielectric substrate. The disk is normally biased by a magnetic field that is provided by two permanent magnets below and above the structure. A two-section feeding network is used to feed the antenna. The operation frequency of the antenna can be adjusted by changing the magnitude of the applied magnetic bias. The sense of polarization can be reversed by reversing the direction of the applied bias. © 2020 Elsevier B.V  

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... 

Task-based self-organizing algorithms have been proposed as a solution for the management of mobile ad-hoc networks (MANETs). Such algorithms assign tasks to nodes by sequentially selecting the best nodes as leaders. Since the correct functionality of such algorithms depends on the truthfulness of participant nodes, any misbehavior can disrupt the operation of the network due to absence of a centralized monitoring unit. In this paper, we consider the problem of malicious behavior in leader-based MANETs. Current solution analyzes the behavior of the leader by means of some checker nodes. This approach is vulnerable since a malicious checker can ruin the character of a normal behaving leader,...