Sharif Digital Repository

Network marketing is a business model that depends upon a network of distributors for growth, such as in multilevel marketing. A direct selling method features independent agents that make up a distribution network for goods and services. This paper provides a framework to study the network marketing by adopting the traditional channel. To motivate all distributers in network marketing as well as retailers, it is required to design a well-balanced distribution and pricing system. The allocated commission for distributers in different layers of network marketing is part of pricing system, which is vital. In this paper, we develop an approach to determine all elements of system, including... 

Time-dependent origin-destination (TDOD) demand is a key input of dynamic traffic assignment (DTA) in advanced traffic management systems. Model reliability is highly dependent on the accuracy of this information. One method to achieve TDOD demand matrices is to use a primary demand matrix and traffic volume counts in some links of a network. This paper proposes a bi-level model to correct the TDOD demand matrix. The extended gradient method (EGM) - an iterative method that minimizes the discrepancy between the counted and estimated traffic volumes - is a suggested means to solve this problem. The methodology is first tested on a small synthetic network to verify its performance. Then, it is... 

The equilibrium crystal structure and electronic structure of BaFe2-x Cox As2 (x = 0,1, 2) superconductor have been investigated by using the pseudopotential Quantum Espresso code based on the ab initio density functional theory in the generalized gradient approximation. The equilibrium crystal structure for x = 1.0 has been determined by considering five different Fe/Co configurations. This study shows that the spin calculation is essential to obtain the experimental values at x = 0.0. The total and partial density of states, band structure, and Fermi surfaces of the three compounds has been calculated. Density of states calculation indicates the important... 

In this paper, a new on-line handwritten signature verification system using Hidden Markov Model (HMM) is presented. The proposed system segments each signature based on its perceptually important points and then computes for each segment a number of features that are scale and displacement invariant. The resulted sequence is then used for training an HMM to achieve signature verification. Our database includes 622 genuine signatures and 1010 forgery signatures that were collected from a population of 69 human subjects. Our verification system has achieved a false acceptance rate (FAR) of 4% and a false rejection rate (FRR) of 12%. © 2003 IEEE  

A significant challenge of foam injection is the stability of the foam in formations. In this study, the modeling of liquid drainage and the impact of some parameters (i.e., concentration of surfactants, nano-particles, and monovalent ions) on the liquid drainage rate and foam stability were investigated by using a population balance model. First, foam bubble size distribution was experimentally measured and used as input for the population balance model. The population balance equations were solved numerically, and the number density of bubble size distribution as a function of time was obtained. Then, the liquid drainage rate was calculated using volume balance equations. It is shown that... 

Electrophoretic motion of hydrophobic particles has been scrutinized numerically in solid-state nanopores. The Poisson, Stokes, and Nernst-Planck equations are solved simultaneously, and the Newton-Raphson algorithm is used to compute the correct velocity at each point. For the hydrophobic surface characterization, the Navier-slip boundary condition with a wide range of slip lengths is applied to the nanoparticle's surface. The effects of the electric field intensity, the electrolyte concentration, and the particle's size on the electrophoretic velocity are examined. Then, the nanopore's size and surface charge density are manipulated to achieve the configuration for separating hydrophobic... 

Electrochemical oxidation of acetaminophen (N-acetyl-p-aminophenol) (1) has been studied in the presence of dimethylamine (2) as a nucleophile in aqueous solution, by means of cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of electrochemically generated N-acetyl-p-quinoneimine (1a) in Michael reaction with dimethylamine (2). Based on ECE mechanism, the observed homogeneous rate constant (kobs) of the above mentioned reaction is estimated by comparing the experimental cyclic voltammograms with the digital simulated results. Further more; kinetics and mechanism of the reaction were studied with ab initio calculation, Monte Carlo and QM/MM... 

In this paper the process of knowledge accumulation for a particular technology is studied. Two countries, say the technology follower and the technology frontier, are considered. The frontier's knowledge growth is determined by its R&D efforts on the technology. The level of knowledge stock for the follower country is augmented by its R&D activities for the technology and absorbing some of the external knowledge through spillover from the frontier. The extent to which the follower is able to exploit the external knowledge depends on technological gap, absorptive capacity, absorption time and degree of spillover. New concepts such as natural and enhanced degree of spillover, background and... 

The paper presents further experiments with an extended version of a comprehensive model for assessment of energy technologies and research and development (R&D) planning to evaluate the impact of innovation programs on development of Iranian electricity-supply system. This analytical instrument is a model of energy R&D resource allocation with an explicit perspective of developing countries which has been linked to a bottom-up energy-systems model. Three emerging electricity generation technologies of solar PV, wind turbine and gas fuel cell are considered in the model and the impact of innovation programs on cost-reducing innovation for them is examined. The main results provided by the... 

The present study aims at monitoring the bulk and bubble-scale behaviour of anionic polyacrylamide-sodium dodecyl sulphate stabilized foam in the absence and presence of oil. Dynamic stability tests provided results indicating that polymer increases the foam dynamic stability and decreases the drainage. Oil slows down the drainage rate of polymer-surfactant foam. In the absence of oil, foam is drained gradually/smoothly whereas remarkable fluctuations are evident in drainage graphs when oil is present. The Hele-Shaw cell was employed to conduct bubble-scale as well as statistical analyses on how foam texture is influenced by a polymer-surfactant system and hydrocarbon. Bubble-scale analyses,... 

Optimal allocation of resources for R&D on new energy technologies is an important issue in the process of development of energy system models. In this study, a model of R&D planning in energy sector has been developed and it is then linked to the energy system model. Energy system model is used as a tool for the technology assessment and prioritization of new energy technologies is evaluated with the help of this model. Based on the economic and environmental impact of new technologies, the optimal allocation of resources for R&D of new technology is estimated with the help of the R&D planning model. The conceptual formulation of the model and its integration with the energy technology... 

In this work, sessile drop and low-bond axisymmetric drop shape analysis methods were coupled to provide some new aspects on stick-slip behavior as well as stick time of a drop on calcite surfaces. Slightly hydrophobic calcite surfaces typified with three irregular roughnesses were used to create irregular surfaces to mimic defects for the water-calcite-air systems. Polishing papers of 200, 600, and 1200 grit and a polishing machine were used to prepare surfaces. X-ray diffraction, energy dispersive X-ray spectroscopy, Fourier transform infrared, and atomic force microscopy techniques were employed to evaluate the chemical and physical properties of surfaces. A model was developed to predict... 

Despite the abundant renewable energy sources, the Iranian energy sector relies almost entirely on fossil fuel energy resources. Power sector is dominant source of CO2 emissions and responsible for about 35% of total CO2 emissions in the country. Additionally, long-term electricity demand of Iran is expected to grow quickly, which in turn requires extensive investment to meet the growing demand over the next decades. On the other hand, increasing domestic fossil fuel consumption had been a serious challenge due to high costs of oil and gas. Current study pays particular attention to the possible penetration rates of renewable electricity technologies and their implications for fossil fuel... 

Data are presented on the solidification of aluminum alloys and their macro segregation behavior. Three alloys with different solidification ranges were prepared in two temperatures. Two types of molds were also prepared by sand and metallic materials. The solidification of Al alloys were studied and the effects of four parameters were determined, including cooling rate, casting temperature, degassing and nucleation effects on solidification and a comparison was conducted to Scheil model performance. Three types of aluminum alloys (Al-12.1%Si, Al-6.9%Si and Al-4.4% Cu) with short, medium and wide solidification ranges were studied and the results showed that degassing, nucleation, increasing... 

A new model is developed for the structure of nanocrystalline materials. Based on the developed model, a new approach for investigating the effect of grain size on the elastic moduli of nanocrystalline materials is introduced. The predictions of the model are strongly correlated with the experimental results reported in the existing literature  

Privacy preservation in wireless sensor networks has drawn considerable attention from research community during last few years. Emergence of single-owner, multi-user commercial sensor networks along with hostile and uncontrollable environment of such networks, makes the security issue in such networks of a great importance. This paper concentrates on token-based privacy preservation schemes. A possible attack on such schemes has been introduced. Two different approaches has been utilized to mitigate the attack. We present mathematical models for it's effects and overheads. The results have been verified using extensive simulations  

In this study, some new aspects of adsorption of a fluorochemical onto carbonate rocks as a wettability alteration agent to a gas wetting condition with the potential application for reduction of condensate blockage in gas condensate reservoirs are presented. To achieve this, kinetics, equilibrium, and thermodynamic of the adsorption process besides contact angle, imbibition, and characterization tests are investigated. Results of adsorption experiments revealed that kinetics behavior of the utilized fluorochemical–calcite system obeyed the pseudo-second order kinetics model. There was no change in adsorption after about 20 h. Also, the intraparticle diffusion mechanism was not the only rate... 

Kinematic mismatch between exoskeletons and human body results in excess internal forces/torques and hence discomfort as well as increase the power consumption. The connection stiffness has been shown to have potentials for minimizing the kinematic mismatch effects. However, realization of a desired stiffness in the connection element seems difficult if not impractical. In this work, adding controlled backlash to the exoskeleton-body connection is investigated as a possible solution for the kinematic mismatch challenge. A stiffness model which includes backlash parameters was formulated and identified experimentally using three male subjects on a typical lower extremity exoskeleton. A...