Sharif Digital Repository

In this study, we investigate the use of catalytic copper-silver-palladium substrates for the growth of multiwalled carbon nanotubes via the thermal chemical vapor deposition. These layers are comprised of nanocrystals of Cu2O, CuO, Ag, Pd, Cu, and PdO and were grown using a DC magnetron sputtering method. Scanning electron microscopy characterizations confirmed the significant growth of carbon nanotubes on the catalytic layer. A comparison of the growth of nanotubes indicated that the thickness of the catalytic layers has a significant impact on the quality and the diameter of the carbon nanotubes. Two major peaks were seen in the Raman spectrum. The formation of graphite multiwalled... 

Energy harvesting has been developed as an effective technology for communication systems in order to extend the lifetime of these systems. In this work, we consider a single-user energy harvesting wireless communication system, in which both of the arrival data and the harvested energy curves are modeled as continuous functions. Our goal is to find an offline algorithm, which maximizes the amount of data which is transmitted to the receiver node by a given deadline. If more than one scheme exist that transmit the maximum data, we choose the one with minimum utilized energy at the transmitter node  

Energy harvesting has been developed as an effective technology for communication systems in order to extend their lifetime. In this paper, we consider a single-user energy harvesting wireless communication system, in which arrival data and harvested energy curves are modeled as continuous functions. Our first goal is to find an offline algorithm, which maximizes the amount of data, which is transmitted to the receiver node by a given deadline. If more than one scheme exists that transmits the maximum data, we choose the one with minimum utilized energy at the transmitter node. We find this optimal algorithm, by showing its properties. Next, we propose an online algorithm for this system and... 

In communications, the nodes with the ability of harvesting energy potentially can prolong the overall network lifetime. In this paper, we consider a single-user energy harvesting wireless communication system, in which arrival data and harvested energy curves are modeled as continuous functions. Our goal is to find an online algorithm for the throughput maximization problem, which only needs the causal information of the arrival processes. We propose a heuristic online algorithm which is efficient for both discrete and continuous models, even when the distributions of harvested energy and arrival data are unknown  

Energy harvesting (EH) has been developed to extend the lifetimes of energy-limited communication systems. In this letter, we consider a single-user EH communication system, in which both of the arrival data and the harvested energy curves are modeled as general functions. Unlike most of the works in the field, we investigate the online algorithms which only acquire the causal information of the arrival data and the harvested energy processes. We study how well the optimal online algorithm works compared with the optimal offline algorithm, and thus our goal is to find the lower and upper bounds for the ratio of the completion time in the optimal online algorithm to the optimal offline... 

This paper investigates the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid. The equilibrium radii of the bubbles are assumed to be smaller than 10 μm at a frequency of 37 kHz in various strong driving acoustical fields around 2.0 bars (1 bar=10 5 Pa). The secondary Bjerknes force is investigated in uncoupled and coupled states between the bubbles, with regard to the quasi-adiabatic model for the bubble interior. It finds that the value of the secondary Bjerknes force depends on the driven pressure of sulfuric acid and its amount would be increased by liquid pressure amplitude enhancement. The results show that the... 

A complete study of the hydrodynamic force on a moving single bubble sonoluminescence in N-methylformamide is presented in this work. All forces exerted, trajectory, interior temperature and gas pressure are discussed. The maximum values of the calculated components of the hydrodynamic force for three different radii at the same driving pressure were compared, while the optimum bubble radius was determined. The maximum value of the buoyancy force appears at the start of bubble collapse, earlier than the other forces whose maximum values appear at the moment of bubble collapse. We verified that for radii larger than the optimum radius, the temperature peak value decreases  

Low-noise amplifiers (LNAs) with low-noise performance are critical components in communication systems. However, reaching a high level of performance is difficult. This study introduces a LNA for radio frequency front-end receivers with a frequency range of 6–12 GHz. The planned LNA contains a two-stage high-electron-mobility transistor cascade amplifier with a minimum measured noise figure of 0.8 dB and a peak gain of 25 dB at room temperature. The proposed LNA is based on a gallium arsenide field-effect transistor transistor (CE3512K2) because of its good low-noise performance at microwave frequency bands. The measured results demonstrate that the proposed LNA is perfectly matched over... 

Photocatalytic decolorization of methylene blue (MB) in aqueous solution was investigated using ZnO nanoparticles immobilized on glass plate. The ZnO nanoparticles were prepared by solution combustion method (SCM) using zinc nitrate as oxidant and glycine as fuel. In the slurry ZnO system the separation and recycling of the photocatalyst is practically difficult. Thus, the ZnO nanoparticles were immobilized on glass supports to solve this problem. The effects of process parameters like, catalyst loading, initial dye concentration, and UV-radiation intensity have been investigated. The best results of MB removal were reported in the 1800 μW cm-2 UVC using two layers immobilized ZnO... 

In present work, a novel supported bucky paper (BP) membrane was fabricated and evaluated for humic acid (HA) removal from water. For better understanding the effect of operating variables, response surface methodology (RSM) was also applied. Three independent parameters namely TOC concentration (5, 10 and 15 mg l-1), operating time (10, 20 and 30 min) and transmembrane pressure (TMP) (1, 2 and 3 bar) were selected for TOC removal (%) and permeate flux analysis. The results revealed that the membrane could effectively remove HA primarily through electrostatic repulsion and then adsorption mechanisms. The study also showed that about 65% and 35% of the removed HA were through repulsion and... 

Propagation of a Gaussian x-ray laser beam has been analyzed in collisionless thermal quantum plasma with considering a ramped density profile. In this density profile due to the increase in the plasma density, an earlier and stronger self-focusing effect is noticed where the beam width oscillates with higher frequency and less amplitude. Moreover, the effect of the density profile slope and the initial plasma density on the laser propagation has been studied. It is found that, by increasing the initial density and the ramp slope, the laser beam focuses faster with less oscillation amplitude, smaller laser spot size and more oscillations. Furthermore, a comparison is made among the laser... 

In strong water drive gas reservoirs (WDGRs), the water encroachment in the gas zone has adverse effects on the gas mobility and causes considerable volume of gas to be trapped behind water front; therefore estimation of residual gas saturation after water influx is an important parameter in estimation of gas reservoirs with strong aquifer support. It is difficult to achieve a thorough and exact understanding of water drive gas reservoirs. It depends on several parameters of petrophysical and operational features. In majority of the previous studies about residual gas saturation, the correlations were depended on petrophysical properties such as porosity, permeability, and initial gas... 

In this paper, we have successfully deposited Ag-Cu thin films. Nanoscale morphology and nanotexture were studied using atomic force microscopy (AFM) through fractal and stereometric parameters. Additional algorithms have been developed to study new fractal parameters such as surface entropy, fractal succolarity, and fractal lacunarity. The results revealed that as the deposition time increased, films exposed isotropies between ~65 and 82%, which were correlated to the fractal patterns, where from #3 to #5 there were greater spatial complexities. Moreover, surface roughness increased from #1 to #3, which was observed for both Sq and Sa. Similar behavior was exhibited by the other height... 

Among various two-dimensional carbon allotropes, graphyne has received extensive research attention with outstanding physical features and excellent application prospects for energy storage systems, specifically lithium-ion batteries anode. The mechanical characteristic of the anode affects the performance and durability of the battery during charge/discharge cycles. Therefore, this research investigates the mechanical properties of α -, β -, and γ -graphyne multilayer configurations using the molecular dynamics (MD) simulation approach. The results demonstrate that the mechanical properties of multilayer graphyne do not significantly depend on carbon layers; however, as the layer numbers... 

Porous carbon template decorated with mixed transition metals/metal oxides with tunable architecture is becoming increasingly important and attractive as a kind of novel electrode materials. In this way, mixed-metallic metal-organic frameworks (MOFs) provide an opportunity for fabrication of homogeneous mixed metals/metal oxides distribution in the porous carbon frame without any carbon precursor additive. Also, structures, dimensions and electrochemical performance of MOFs can be readily manipulated by simply tuning the metals molar ratio. In this study, we demonstrate the design and fabrication of petal-like NiCo/NiO-CoO metal/metal oxides with a rational composition embedded in 3D... 

Dirac leaky-wave antennas (DLWAs) are derived from photonic crystals exhibiting Dirac cone dispersion around their Γ-point. DLWAs provide high directive beams and continuous frequency beam scanning, non-fluctuating leakage constant and real non-zero Bloch impedance at and around broadside, due to the closed and linear Dirac dispersion relation around broadside. These features, along with their inherent compatibility for higher frequency designs (larger unit cells compared to metamaterials), make DLWAs an ideal candidate for the upper microwave, mm-wave and terahertz frequencies, and for applications such as radar, 5G, spectroscopy, etc. In this review, we cover the recent developments on... 

Over the last few years, substantial efforts have been made to develop earth-abundant bi-functional catalysts for urea oxidation and energy-saving electrolytic hydrogen production due to their low cost and the potential to replace traditional noble-metal-based catalysts. Nevertheless, finding a straightforward and effective route to prepare efficient catalysts with unique structural features and optimal supports still is a big challenge. Among the various candidates, metal-organic framework (MOF)-derived materials show great advantages as new kinds of active non-precious catalysts. On the other hand, the controllable integration of MOFs and carbon-based nanomaterials leads to further... 

In the majority of leaky-wave antennas (LWAs), the lack of broadside radiation is due to the existence of an open-stopband (OSB) at broadside. In this letter, we present a study on the OSB suppression in LWAs. In particular, we start from a simple unit cell comprising a planar waveguide having alternating open and short sidewalls. The analytical and simulated band structures testify consistently that OSB suppression can indeed be realized by proper design, analytically studied using mode-matching, and further supported by full-wave simulations. An LWA is then implemented using the substrate integrated waveguide (SIW) technology, which provides interesting features such as a high directive... 

Exploring bi-functional electrocatalysts with excellent activity, good durability, and cost-effectiveness for electrochemical hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte is a critical step towards a sustainable hydrogen economy. Three main features such as high density of active sites, improved charge transfer, and optimized electronic configuration have positive effects on the electrocatalyst activity. In this context, understanding structure–composition–property relationships and catalyst activity is very important and highly desirable. Herein, for the first time, we present the design and fabrication of novel MOF-derived ultra-small Ru/RuO2 nanoparticles... 

In this paper, a wideband coupled-resonator microstrip bandpass filter is designed and experimentally demonstrated in the S-Band. The filter is comprised of quarter-wavelength hair-pin resonators, reducing resonator and filter footprint compared to conventional hairpin designs. Additionally, it is considerably forgiving to fabrication tolerances and yields remarkably close matched results between theory, simulation, and measured results. One demonstration presented has minimal insertion loss ${(< 1{dB})}$ for the entire wide bandwidth of 3.4 GHz to 4.2 GHz. Wider bandwidths up to 60% are also observed using the design. The proposed filter is an attractive solution when space is a critical...