Sharif Digital Repository

In this paper the Multiple Relay Channels (MRC) with delays, with and without channel state information (CSI) are investigated from an information theoretic point of view. For the MRC with unlimited look ahead where the relays can use the whole received block to encode, upper and lower bounds on the capacity are derived which are tight for the degraded case. For the MRC without-delay where the relays have access to the present received symbols in addition to the past symbols, the capacity of the degraded channel is established using Shannon's strategy for the channels with side information. Then we introduce the state dependent MRC with unlimited look ahead and derive a lower bound on the... 

We have investigated an oxidation of substrate effect on structural morphology of zinc oxide (ZnO) rods. ZnO rods are grown on porous silicon (PS) and on thermally oxidized porous silicon substrates by carbothermal reduction of ZnO powder through chemical vapour transport and condensation. Porous silicon is fabricated by electrochemical etching of silicon in hydrofluoric acid solution. The effects of substrates on morphology and structure of ZnO nanostructures have been studied. The morphology of substrates is studied by atomic force microscopy in contact mode. The texture coefficient of each sample is calculated from X-ray diffraction data that demonstrate random orientation of ZnO rods on... 

Here, the UV photodetection of ZnO rods grown on porous silicon substrates are reported. Laterally interconnected ZnO rods have been synthesized by chemical vapor transport and condensation method on porous silicon substrates. As characterized by current-voltage measurements the I-V characteristics have linear behavior, indicating space charge effect. The device exhibits photocurrent response of 0.027 A/W for 325 nm UV light under -5 V bias. The rise and decay time constants under these conditions are 19 and 62 s, respectively  

A uniformly distributed ZnO nanowire array has been grown on silicon (100) substrates by catalyst-free chemical vapor transport and condensation. The effect of growth conditions including source heating temperature, substrate temperature, and gas flow rate on growth properties of ZnO nanowire arrays are studied. Scanning electron microscopy, X-ray diffraction, and room temperature photoluminescence are employed to study the structural features and optical properties of the samples. The results show a correlation among experimental growth parameters. There is a zone for substrate temperature, by controlling gas flow rate, that uniformly distributed and well aligned ZnO nanowire arrays can be... 

Here in this research, we report on surface engineering of bulk Cu2O photocathode thorough employing nanostructured materials. Nanorods (NRs) of copper oxide with average lengths of 150 nm have been synthesized by anodization of Cu foil in aqueous KOH electrolyte, followed by annealing treatment. Several heating processes were examined to reach pure Cu2O nanostructures and lastly the moderate annealing procedure at 700 °C under Ar gas flow resulted in pure Cu2O nanostructures, confirmed by XRD analysis. Surface modified nanorod/bulk Cu2O electrode was prepared by spin coating of sediments suspension of anodized drop on bulk Cu2O film fabricated through thermal oxidation method, followed by... 

Soccer model and relation of players and coach has been analyzed by a learning automata-based method, called Soccer Mobility Estimator (SME), who estimates the mobility model of soccer players. During a soccer match, players play according to a certain program designed by coach. The pattern of players' mobility is not stochastic and it can be assumed that they are playing with a certain mobility model. Since knowledge about mobility model of nodes in mobile ad-hoc networks has a substantial effect on its performance evaluation, knowledge about mobility model of soccer players can be useful for coaches and experts for game analysis. In fact the mobility model of players could be an important... 

Aggregated sub-micron size nitrogen doped TiO2 (N-TiO2) particles with superior optical and electrical features were successfully synthesized for embedding into commercial mesoporous TiO2 photoelectrode of dye sensitized solar cells (DSSCs) as the light scattering particles compared to undoped one. X-ray photoelectron spectroscopy and absorption spectra confirmed that the titanium dioxide is sufficiently doped by nitrogen in N-TiO2 sample. Employing these high-surface N-TiO2 in mesoporous photoelectrode of solar cells, the power conversion efficiency of 8% has been achieved which shows 17% improvement for the optimum embedded level of... 

The structural, electrical, optical, and photovoltaic properties of aggregated submicron nitrogen-doped TiO2 particles (NTiO2) and the influence of utilizing them, in comparison with undoped ones, as the light-scattering layer of dye-sensitized solar cells were investigated. Field emission scanning electron microscope, X-ray diffraction, and diffuse reflectance spectra showed that both type samples have similar morphology, crystal phase, and scattering feature. Moreover, photoluminescence, Mott–Schottkey, and photovoltaic characteristics such as IMPS/IMVS and charge extraction analysis indicated that the NTiO2 layer is an efficient scatterer in two aspects: enhancement of light-harvesting... 

The cauliflower like ZnO nanostructures are grown on ZnO nanorods using spray pyrolysis method. First, ZnO nanorod arrays are grown on p-type silicon substrate without catalyst by chemical vapor transport and condensation method in a horizontal tube furnace. Afterwards, the cauliflower like ZnO nanostructures is deposited on top of the ZnO nanorod array. The PL spectra of cauliflower like ZnO nanostructures consist of UV emission bands around 387 nm and a visible emission at ∼440 nm. The current-voltage (I-V) measurement under dark and UV illumination condition are performed to study photodetection of the cauliflower like ZnO-ZnO nanorod/p-Si heterostructure. The experimental data of dark... 

In this study TiO2 nanotubular fibers were prepared and subsequently loaded with CdS nanoparticles to obtain visible light activate nanofibers with modified structure. Preparation of TiO2 fibers was based on templating method and Liquid phase deposition technique (LPD) with cellulose fibers as templates. Using LPD, thickness of the TiO2 layer could be controlled precisely by adjusting the reaction conditions, therefore after removal of the template, the resulting material has a fibrous structure, mimicking the cellulose fibers shape. CdS nanoparticles were synthesized by thermochemical growth method and attached to TiO2 fibers through impregnation method. The pure composite nanofibers were... 

Gas sensors have been fabricated based on field ionization from titanium oxide nanotubes grown on titanium foil. Ordered nanaotube arrays of titanium oxides were grown by the anodization method. We measured breakdown voltages and discharge currents of the device for various gases. Our gas ionization sensors (GIS) presented good sensitivity, selectivity, and short response time. The GISs based on TiO2 nanotube arrays showed lower breakdown voltage, higher discharge current, and good selectivity. An excellent response observed for Ar compared to other gases. Besides, by introducing 2 % CO and 4 % H2 to N2 flow gas, the amount of breakdown voltage shifts about 20 and 70 volts to the lower... 

We have studied the mechanical properties of a few-layer graphene cantilever (FLGC) using atomic force microscopy (AFM). The mechanical properties of the suspended FLGC over an open hole have been derived from the AFM data. Force displacement curves using the Derjaguin–Müller–Toporov (DMT) and the massless cantilever beam models yield a Young modulus of Ec ~ 37, Ea ~ 0.7 TPa and a Hamakar constant of ~ 3 × 10 − 18 J. The threshold force to shear the FLGC was determined from a breaking force and modeling. In addition, we studied a graphene nanoribbon (GNR), which is a system similar to the FLGC; using density functional theory (DFT). The in-plane Young's modulus for the GNRs were calculated... 

Density-functional study of strain effects on the electronic band structure and transport properties of the graphene nanoribbons (GNR) is presented. We apply a uniaxial strain (ε) in the x (nearest-neighbor) and y (second-nearest-neighbor) directions, related to the deformation of zigzag- and armchair-edge GNRs (AGNR and ZGNR), respectively. We calculate the quantum conductance and band structures of the GNR using the Wannier function in a strain range from −8% to +8% (minus and plus signs show compression and tensile strain). As strain increases, depending on the AGNR family type, the electrical conductivity changes from an insulator to a conductor. This is accompanied by a variation in the... 

The electrical bending instability in charged liquid jets is the phenomenon determining the process of electrospinning. A model of this phenomenon is lacking however, mostly due to the complicated interplay between the viscosity and elasticity of the solution. To investigate the bending instability, we performed electrospinning experiments with a solution of polyethylene oxide in water/ethanol. Using a fast camera and sensitive multimeter, we deduced an experimental dispersion relation describing the helix pitch length as a function of surface charge. To understand this relation, we developed a theoretical model for the instability for a wide range of visco-elastic materials, from conducting... 

In this paper, we describe a real-time Gradient-based Multiple Faces Tracking (GMFT) algorithm in complex background. In GMFT method first faces are detected by combination of morphological facial feature extraction and gradient-based edge detection methods. After a face is reliably detected, it is tracked over time with a novel real-time algorithm. The algorithm has been implemented and tested under a wide range of real-world conditions. The resulting system runs in real-time on a standard PC, being robust to face scale variations, rotations in depth, and fast changes in subject/camera position. It has consistently provided performance which satisfies the following requirements: 1) able to... 

Asphaltene precipitation is known to be responsible for serious challenges in oil industry such as wellbore damage, oil flow reduction, and plugging of transportation lines. The traditional methods to remove asphaltene deposition are mostly based on chemical solvent. One of the recent proposed green and cost–effect remedial methods is the application of microorganisms capable of consuming the heavy hydrocarbon chains. The cell surface hydrophobicity among others effectively manipulates the efficiency of the microorganism for asphaltene degradation. Besides, surface active agents would affect the microorganism adhesion and cell surface properties, and alters its hydrophobicity. Investigating... 

Asphaltene precipitation is known to be responsible for serious challenges in oil industry such as wellbore damage, oil flow reduction, and plugging of transportation lines. The traditional methods to remove asphaltene deposition are mostly based on chemical solvent. One of the recent proposed green and cost–effect remedial methods is the application of microorganisms capable of consuming the heavy hydrocarbon chains. The cell surface hydrophobicity among others effectively manipulates the efficiency of the microorganism for asphaltene degradation. Besides, surface active agents would affect the microorganism adhesion and cell surface properties, and alters its hydrophobicity. Investigating... 

We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150–220 °C range as a function of time initially shows linear mass... 

Understanding the dynamics of direct electrospinning is the key to control fiber morphologies that are critical for the development of new electrospinning methods and novel materials. Here, we propose the theory for direct electrospinning based on theories for (liquid) "rope coiling" and experimentally test it. For the experiments, the buckling of microscale liquid ropes formed from polymer solutions is studied systematically using three different electrospinning setups and for different polymer concentrations. We show that different buckling regimes exist, whose dynamics are governed by an interplay of electrical, inertial, and viscous forces, and that three different buckling regimes... 

The spatial scaling law and intermittency of the V2O5 surface roughness has been investigated by atomic force microscopy. The intermittency of the height fluctuations has been checked by two different methods, first, by measuring the scaling exponent of the qth moment of height-difference fluctuations i.e. Cq = <|h(x1) - h(x2)|q>, and second, by defining the generating function Z(q, N) and generalized multi-fractal dimension Dq. These methods predict that there is no intermittency in the height fluctuations. The observed roughness and dynamical exponents can be explained by numerical simulation on the basis of the forced Kuramoto-Sivashinsky equation