Sharif Digital Repository

A kinetic model for growth of ZnO nanorods via vapor-liquid-solid (VLS) mechanism based on the bulk diffusion of Zn atoms through the Au-Zn droplet is presented. The dependences of the growth rate on size are given quantitatively. A general expression for the growth rate of nanorods during VLS process is derived. The derived formula shows the dependences of growth rate on lateral size of nanorods, concentration and supersaturation of Zn atoms in the liquid droplet. Based on the presented kinetic model the smaller nanorods have faster growth rate. Au-catalyzed ZnO nanorods are grown by chemical vapor transport and condensation (CVTC) process experimentally. Theoretical and experimental... 

Short ZnO nanorods and long ZnO nanowires have been produced on SiO2 and Si substrates by VLS and VS mechanisms via a double tube chemical vapor transport and condensation (CVTC) process. The role of reactants and droplet interfaces on the nucleation and growth of ZnO nanorods have been investigated. A conceptual model for nucleation of ZnO nanorods has been proposed by describing the half-oxidation and reduction reactions at the growth front. The importance of Zn vapor in the nucleation phenomena has been studied by changing starting materials. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and EDX analysis have been used to characterize ZnO nanorods and investigate the... 

This paper introduces a new procedure to forecast the future O/D demand. It is a hybrid of logit and Fratar model. The hybrid model has the long run, policy sensitive, characteristic of a logit model, calibrated at sector-level with little/no zero O/D cells. This feature, joint with a Fratar-type operation at zonal level within a sector, gives a better performance to this model than either of the two types of the models alone. The performance of the hybrid model is contrasted with a neural network model, and shows encouraging results in a real case  

The present study was carried out to evaluate the degradation efficiency of benzene, toluene, and xylene (BTX) by isolated bacteria from various petroleum-hydrocarbons contaminated sites. Five isolated bacteria were selected for testing BTX biodegradation from liquid culture media. Each of these bacteria was able to degrade BTX but with different efficiencies. Maximum biodegradation efficiency for benzene (more than 70 %) was obtained by Gram-positive coccobacillus, Gram-positive coccus and Gram-negative bacillus bacteria, for toluene (60 %) and xylene (70 %) by Gram-positive coccobacillus and Gram-negative coccobacillus. It was found that the presence of xylene in the substrate mixture... 

This paper is a complete survey of flowshop-scheduling problems and contributions from early works of Johnson of 1954 to recent approaches of metaheuristics of 2004. It mainly considers a flowshop problem with a makespan criterion and it surveys some exact methods (for small size problems), constructive heuristics and developed improving metaheuristic and evolutionary approaches as well as some well-known properties and rules for this problem. Each part has a brief literature review of the contributions and a glimpse of that approach before discussing the implementation for a flowshop problem. Moreover, in the first section, a complete literature review of flowshop-related scheduling... 

The biodegradability rates of two different kinds of polyethylene bonded with corn and potato starch are studied in this paper. While it is usual to use soil as the environment for biodegradation, an aerated sludge tank was used in this studywhich offers a richermicrobialmediumand increases the rate of biodegradation. The biodegradability is determined by two ways: first, comparing differences in the weight change of two samples, one placed inside distilled water and the other placed in aerated sludge tank. Second test for biodegradation is by examination of FTIR spectroscopy. Through FTIR spectroscopy, the biodegradability rate and reduction in some of the existing bonds in polymer before... 

In this study Fe3O4/CMC magnetic nanoparticles were synthesized through co-precipitation method. Afterward, laccase from Trametes hirsuta was immobilized onto Carboxymethyl cellulose (CMC)-coated magnetic Fe3O4 nanoparticles by covalent bonding between carboxyl groups of carboxymethyl cellulose and amine group of laccases. Also, the resulted magnetic nanoparticles and immobilized laccase were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and dynamic light scattering (DLS) analysis. Moreover, the vital factors in enzyme immobilization, such as contact time, amount of N-hydroxysuccinimide (NHS), and the amount of nanoparticles were... 

In this work, we used λ-DNA to produce metallic DNA samples and we investigated the stabilization time of their impedances. This is in order to show that the DNA molecules can possibly be utilized as a frame for assembling the nanocircuits and as an electronic element as well, in nanoelectric devices. It has been shown that metallic DNA has lower stabilization time than natural DNA. As expected, it is shown that making the bundled DNA oriented, impacts their impedance stabilization. In order to find the characteristic impedance of the DNA molecules under direct current, we designed and made patterned electrodes to make electrical connections between the DNAs and the used current source. The... 

In this study the effect of HPGR operational parameters on the dimensional properties of pellet feed was examined and optimized using factorial methodology. The operational parameters considered include feed moisture, specific pressure and roll speed. For this study, size and shape of particles with Blaine number in the range 1800–2200 cm2 g−1 was thoroughly investigated. It was deduced that increasing the specific pressure and decreasing the roll speed would result in reduction of D80 but would increase the Blaine number. The circularity, aspect ratio and roughness descriptors of the particles were measured by SEM micrographs and image analysis software. It was observed that particles... 

In this study the effect of HPGR operational parameters on the dimensional properties of pellet feed was examined and optimized using factorial methodology. The operational parameters considered include feed moisture, specific pressure and roll speed. For this study, size and shape of particles with Blaine number in the range 1800–2200 cm2g−1 was thoroughly investigated. It was deduced that increasing the specific pressure and decreasing the roll speed would result in reduction of D80 but would increase the Blaine number. The circularity, aspect ratio and roughness descriptors of the particles were measured by SEM micrographs and image analysis software. It was observed that particles tended... 

This paper develops a novel insight and procedure that includes a variety of algorithms for finding the best solution in a structured multi-agent system with internal communications and a global purpose. In other words, it finds the optimal communication structure among agents and the optimal policy in this structure. First, a unique reinforcement learning algorithm is proposed to find the optimal policy of each agent in a fixed structure with non-linear function approximators like artificial neural networks (ANN) and with eligibility traces. Secondly, a mechanism is presented to perform self-organization based on the information of the learned policy. Finally, an algorithm that can discover... 

The change of gait pattern and muscular activity following amputation is thought to be responsible for the higher incidence of joint degenerative disorders observed in amputees. Considering the lack of consistent data in the literature, the purpose of the present study was to measure and analyze the spatio-temporal variables, the kinematics and, particularly, the net joint moments of the intact and prosthetic limbs of above knee amputee subjects during walking and to compare the results with those of normals. The gait characteristics of five transfemoral amputees and five normal subjects were measured using videography and a force platform. The human body was modeled as a 2-D sagittal plane... 

Cement kiln dust (CKD) is one of the most important waste materials in the cement industry. The large amount of this material, has encouraged researchers to propose new ways to recycle and reuse it. In this paper, effects of adding cement kiln dust to the ordinary Portland cement, on the physical and mechanical properties of ordinary and lightweight concrete were investigated. Results showed that concrete containing CKD, presents lower workability and modulus of elasticity; however, improvements in strength was observed by adding particular amounts of CKD. Eventually, it was found that adding 10% of cement weight CKD is the appropriate percentage for utilizing in manufacturing ordinary and... 

Particle size and shape of iron ore concentrate are effective parameters in the production of quality green pellets. In this research, the effect of particle morphology on green pellet quality was studied. It was concluded that pellet quality improved with increasing specific surface area. Drop number and green compression strength of pellets ground by HPGR were found to be superior over those ground in the ball mill. The chief reasons were related to particle shape and the fraction of fine particles. Smaller particle size results in a higher order of bonding between particles and therefore the formation of a stronger system. Also, the rougher and less circular shape of particles resulted in... 

In this paper, we propose a new transmission scheme, called integer forcing-and-forward (IFF), for communications among multipair multiple-antenna users in which each pair exchanges their messages with the help of a single multiple-antenna relay in the multiple-access and broadcast phases. The proposed scheme utilizes integer forcing linear receiver (IFLR) at the relay, which uses equations, i.e., linear integer combinations of messages, to harness intrapair interference. Accordingly, we propose the design of a mean square error (MSE)-based transceiver, including precoder and projection matrices for the relay and users, assuming that perfect channel state information (CSI) is available. In... 

The compute-and-forward (CMF) method has shown a great promise as an innovative approach to exploit interference towards achieving higher network throughput. The CMF was primarily introduced by means of information theory tools. Although there have been some recent works discussing different aspects of efficient and practical implementation of CMF, there are still some issues that are not covered. In this study, the authors first introduce a method to decrease the implementation complexity of the CMF method. They then evaluate the exact outage probability of the authors proposed simplified CMF scheme, and hereby provide an upper bound on the outage probability of the optimum CMF in all... 

In the present research, we investigate the synergistic effects of Ru-doping and Ar/H2 reduction treatment on the photoelectrochemical water splitting performance and hydrogen evolution rate of TiO2 nanotube array photoelectrodes. The Ti-Ru alloy with 0.2 at. % Ru was used to grow anodic self-organized Ru-doped TiO2 nanotube layers. An ideal synergy between Ar/H2 reduction treatment and Ru-doping results in the extended absorption toward the visible light region and improved photoelectrocatalytic activity. The black Ru-doped TiO2-x photoanode's water splitting rate improves remarkably (∼ninefold) compared to the black TiO2-x sample (∼twofold). Moreover, the black Ru-doped TiO2-x photoanode... 

We propose a novel cooperative transmission scheme called Convolutional Network-Coded Cooperation (CNCC) for a network including N sources, one M-antenna relay, and one common destination. The source-relay (S-R) channels are assumed to be Nakagami-m fading, while the source-destination (S-D) and the relay-destination (R-D) channels are considered Rayleigh fading. The CNCC scheme exploits the generator matrix of a good (N + M', N,v) systematic convolutional code, with the free distance of dfree designed over GF(2), as the network coding matrix which is run by the network's nodes, such that the systematic symbols are directly transmitted from the sources, and the parity symbols are sent by the...