Sharif Digital Repository

In this paper, the problem of resource allocation at an Ad hoc network with nodes not using any infrastructure to cooperate with each other is considered. By using a simple interference model in wireless links, the convergence and stability of a fair resource allocation scheme in the absence of delay is investigated. Also, the local stability of the scheme in the presence of upper-bounded delay is verified. Simulations results illustrate the convergence and fairness of this scheme considering different initial states for different sources. The performance of the scheme in the presence of different disturbances for each flow in transient and steady state along with its local stability in the... 

TiO2/ZnO and ZnO/TiO2 nanolayer thin films were synthesized using sol-gel method. Optical analysis revealed high transmittance of the films in the visible range with almost the same bandgap energy for the both systems. XPS technique shows stoichiometric formation of TiO2 and ZnO on the surface of TiO2/ZnO and ZnO/TiO2 layers, respectively. According to AFM observations and its data analysis, the TiO2/ZnO films exhibited a higher surface roughness and more effective interfaces with electrolyte during redox reactions. Based on photoelectrochemical measurements, TiO2/ZnO nanolayer photoanode possesses a lower charge transfer resistance and higher transient time for charge carriers (e- and h+)... 

In this study, the effects of TiO2 addition on the physical and photoelectrochemical properties of ZnO thin films have been investigated. The (TiO2)x-(ZnO)1-x nanocomposite thin films were dip-coated on both glass and indium tin oxide (ITO)-coated conducting glass substrates with various values of x, specifically 0, 0.05, 0.1, 0.25 and 0.5. Optical properties of the samples were studied by UV-vis spectrophotometry in the range of 300-1100 nm. The optical spectra of the nanocomposite thin films showed high transparency in the visible region. The optical bandgap energy of the (TiO2)x-(ZnO)1-x films increased slightly with increasing values of x. The crystalline structure of the nanocomposite... 

In this investigation, the effect of annealing temperature and concentration of gold nanoparticles on the photoelectrochemical properties of sol-gel deposited Au : TiO2 nanocomposite thin films is studied. Various gold concentrations have been added to the TiO2 thin films and their properties are compared. All the deposited samples are annealed at different temperatures. The optical density spectra of the films show the formation of gold nanoparticles in the films. The optical bandgap energy of the Au : TiO2 films decreases with increasing Au concentration. The crystalline structure of the nanocomposite films is studied by x-ray diffractometry indicating the formation of gold nanocrystals in... 

Printing technologies are gaining growing attention as a sustainable route for the fabrication of high-performance and flexible power sources such as microsupercapacitors (MSCs). Here, the inkjet printing method is utilized for the fabrication of manganese dioxide (MnO2)-based, flexible all-solid-state MSCs on surface-modified A4 paper substrate. The appropriate rheology of the formulated ethanol-based ink (Fromm number <10) and the proper dimensions of MnO2 nanoflowers (average size ∼600 nm) ensure a reliable inkjet printing process. Moreover, the underlying graphene/Ag nanowire pattern serves as a primer and highly conductive (Rs < 2 Ω sq-1) layer on top of the paper to facilitate the... 

Due to rapid population growth, industrialization, and urbanization, both discharged wastewaters are rich in various pollutants, and energy crises are two of the world's leading challenges. Simultaneous photocatalysis to produce H2 from wastewater treatment is a promising approach for addressing both global environmental and energy problems at the same time. As a step toward achieving this goal, designing visible-light-active photocatalysts has been an appealing approach in dual-functional photocatalytic reactions via heterojunction formation and cocatalyst utilization. In this study, organic pollutants, namely dyes, drugs, and biomass, will be examined to produce hydrogen from these... 

Providing solar hydrogen as a clean energy resource is one of the human challenges for future. Controlling oxygen vacancies as well as surface morphology in metal oxide semiconductors enables developing PEC H2production in some understood ways. Here, the influence of simple change in annealing atmosphere, air and pure oxygen, on photoresponse of nanocrystalline WO3has been studied completely. Results revealed that such slight change in annealing procedure increases effective surface interface and donor density by 77 and 72%, respectively. These effects and also retarding recombination of photogenerated electro-hole pair resulted in photocurrent enhancement under solar like illumination more... 

ZnO/gC 3 N 4 hybrid nanofibers containing different concentrations of gC 3 N 4 nanosheets were prepared using electrospinning technique; this was followed by annealing at 460 forC for one hour in a box furnace. Based on scanning electron microscopy (SEM) image analysis, the mean diameter of the nanofibers was measured to be ~ 55 nm. Fourier transform infrared (FTIR) spectroscopy confirmed the presence of ZnO and gC 3 N 4 in the prepared nanofibers. The photocatalytic activity of the nanofibers was examined under UV photoirradiation, showing that the ZCN0.5 nanofibers containing 0.5 wt% of gC 3 N 4exhibited the highest performance, as compared to other photocatalysts. The observed improvement... 

Abstract: Photocatalysis using semiconductors has emerged as a promising wastewater treatment process to overcome the major challenges faced by conventional technologies. The advantages of ZnO nanomaterials over other semiconductors, and their structure-dependent properties, make them important building blocks in nanotechnology as multifunctional materials. Moreover, it has been confirmed that ZnO nanomaterials can exhibit high performance in photodegradation of organic dyes for treatment of industrial effluent. The wurtzite structure of ZnO contains polar and nonpolar planes; the low surface energy and thermodynamic stability of the nonpolar planes enable formation of one-dimensional (1D)... 

The physical and photoelectrochemical properties of the anodized ZnO-TiO2 thin films were investigated in this study. Impedance spectroscopy revealed a decrease in charge transfer resistance and Tafel plots determined enhancement of about 200 times in the exchange current (i 0) after anodization at high positive potential. It was found from XPS analysis that after applying the potential of 5 V to the ZnO-TiO2 photoelectrode, the lattice oxygen (O2-) in the thin film is oxidized to molecular oxygen and then, cations such as Zn2+ can be solved in the basic electrolyte and passed to the solution. Moreover, according to AFM analysis it was observed that the surface of the samples has been... 

Energy and environment crises motivated scientists to develop sustainable, renewable, and clean energy resources mainly based on solar hydrogen. For this purpose, one main challenge is the low cost flexible substrates for designing earth abundant efficient cocatalysts to reduce required water oxidation overpotential. Here, a systematic morphological and electrochemical study has been reported for cobalt oxide/hydroxide nanoflakes simply electrodeposited on four different commercially available substrates, titanium, copper sheet, steel mesh, and nickel foam. Remarkable dependence between the used substrate, morphology, and electrocatalytic properties of nanoflakes introduced flexible porous... 

Solar energy generation is one of the most efficient approach to solve emerging environment and energy challenges. In this context, solar assisted dissociation of water into oxygen and hydrogen utilizing scalable and high performance electrocatalysts plays key role since the produced hydrogen is a clean energy carrier. Here, cobalt based nanoflakes with metallic core and oxidized surface were grown on the designed carbonaceous layer for anodic oxygen evolution reaction (OER) using an electrochemical approach. Carbonaceous layers containing proper amount of carbon nanotubes (CNT) and reduced graphene oxide (rGO) species were used to optimize the system. Although higher weight percent of rGO... 

Cancer is one of the most significant causes of death in the world. It has been shown that the role of circulating tumor cells (CTCs) in the early detection of cancer is crucial. Since the number of these cancerous cells in blood is very rare, the inertial microfluidic devices are one of the best candidates for the isolation of CTCs because they result in a high throughput process. Consequently, they can process a large volume of blood in a short time. Despite extensive computational and experimental studies on inertial microfluidic platforms, the impact of the curvature has not been thoroughly investigated during separation. In this paper, the feasibility of isolation of CTCs for... 

The increasing trend of integrating Renewable Energy Sources (RESs) into power systems could cause operational challenges in the system from flexibility and reliability perspectives. Respectively, utilities would be relied on local flexible resources to address the flexibility requirements in power systems. In this respect, local resources in distribution systems could participate in ancillary markets along with the wholesale energy markets to address the flexibility capacity shortage in the system. Consequently, this paper aims to provide a framework to optimize the scheduling of resources in distribution networks while participating in energy, regulation, and ramp markets. Correspondingly,... 

Photocatalytic wastewater treatment and concurrent energy production or metal ions conversion to less harmful products have great potential to address both environmental and energy challenging issues, two of the most significant problems facing humankind. Many efforts have been devoted for achieving enhanced photocatalytic activity as well as optimizing reaction conditions and materials design. In this context, various strategies were applied to develop efficient dual-functional photocatalysts for environmental purification and simultaneous energy production. Concurrent photocatalytic degradation of organic pollutants and Cr(VI) reduction to less toxic Cr(III) improved the rate of both... 

Oil viscosity plays a key role in reservoir simulation and production forecasting, as well as planning thermal enhanced oil recovery methods and these make its accurate determination necessary. In this communication, the most frequently used oil viscosity correlations are evaluated using a large databank of Iranian oil reservoirs which were measured using a Rolling Ball viscometer (Ruska, series 1602). To evaluate the performance and accuracy of these correlations, statistical and graphical error analyses have been used simultaneously. Three of the most accurate correlations for each region, including dead oil viscosity, viscosity below bubble point, viscosity at bubble point and the... 

A new synergetic hybrid Ag/ZnO nanostructure was fabricated which is able to cause photocatalytic degradation (in high yields) of methylene blue under visible light as well as in the dark. In this nanostructure, ZnO was synthesized using the arc discharge method in water and was coupled with Ag via a chemical reduction method. X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy results confirmed the existence of defects in ZnO in the hybrid nanostructures; these defects act as electron traps and inhibit the recombination of electron-hole pairs. The absorption edge of the hybrid nanostructure shifts toward the visible region of the spectrum due to a combination of the Ag... 

NiAl-TiC composites were synthesised by volume combustion (VC) method from elemental powders to improve the mechanical properties and high temperature performance of nickel aluminide. Synthesised specimens with porous nature were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. XRD results showed that NiAl was dominant phase and other phases like Al 3 Ni 2 (in NiAl + 5 wt-% TiC, NiAl + 10 wt-% TiC specimens) and AlNi 3 (in equimolar NiAl-TiC) were present in specimens. Synthesised specimens of NiAl, NiAl + 5 wt-% TiC, NiAl + 10 wt-% TiC, NiAl + 15 wt-% TiC and equimolar NiAl-TiC achieved Vickers... 

Development of simple yet precise sensing platforms for rapid determination of biological species and drugs is of paramount importance, not only for analysis of pharmaceutical formulations during the production stage, but also in clinical practices and medical diagnosis. In the present research, we report on the electrochemical determination of atorvastatin (ATOR) by using silver nanowires/gold-modified glassy carbon electrode (Ag NWs/Au/GCE). The modified electrode was constructed through a two-step procedure in which narrow silver nanowires synthesized via a polyol method are drop casted on a pre-modified GCE with electrodeposited gold particles. The results of XRD analysis indicated the... 

One of the most elusive problems in quantum mechanics is the transition between classical and quantum physics. This problem can be traced back to Schrödinger's cat thought experiment. A key element that lies at the center of this problem is the lack of a clear understanding and characterization of macroscopic quantum states. Our understanding of macroscopic quantumness relies on states such as the Greenberger-Horne-Zeilinger (GHZ) or the NOON state. Here we take a first-principle approach to this problem. We start from coherence as the key quantity that captures the notion of quantumness and require the quantumness to be collective and macroscopic. To this end, we introduce macroscopic...