Sharif Digital Repository

In this paper, we propose a distributed rate and power allocation algorithm for real time traffic by using second order statistics of the channel. Our method minimizes the average delay of transmission over the fading channel. We assume that each sub carrier relies on its own buffer, and a constant arrival rate from higher layer application arrives at input buffers of each sub-carrier. This constant rate is optimally distributed through individual sub-rates transmitted over each sub-channel. Optimum power coefficients are also derived to minimize the average delay of transmission. In addition, collision and buffer overflows are taken into account while achieving acceptable throughputs  

The everlasting bandwidth limitations in wireless communication networks has directed the researchers' thrust toward analyzing the prospect of overloaded Code Division Multiple Access (CDMA). In this paper, we have proposed a Genetic Algorithm in search of optimum signature matrices for binary-input synchronous CDMA. The main measure of optimality considered in this paper, is the per-user channel capacity of the overall multiple access system. Our resulting matrices differ from the renowned Welch Bound Equality (WBE) codes, regarding the fact that our attention is specifically aimed at binary, rather than Gaussian, input distributions. Since design based on channel capacity is... 

Cooperation is an integral part of wireless ad hoc networks. In this paper, we introduce a combination of pricing and reputation-based mechanisms targeted at generating higher incentive for cooperation among nodes. The reputation-based part of the mechanism guarantees proper cooperation among sources. In addition, the pricing-based mechanism is added to ensure cooperation of relay nodes. In contrast with earlier works, a more comprehensive definition of cooperation is presented which guarantees a better reward and punishment system. In our approach, a multi-player game is defined with continuous strategy set and payoffs which lead to a more practical model. Based on the proposed game... 

An accurate thermal model to predict the heat generation in rechargeable batteries is an essential tool for advanced thermal management in high power applications, such as electric vehicles. For such applications, the battery materials' details and cell design are normally not provided. In this work a simple, though accurate, thermal model for batteries has been developed, considering the temperature- and current-dependent overpotential heat generation and State-of-Charge dependent entropy contributions. High power rechargeable Li-ion (7.5 Ah) batteries have been experimentally investigated and the results are used for model verification. It is shown that the State-of-Charge dependent... 

In the present work, a novel microextraction method named in situ solvent formation microextraction (ISFME) using ionic liquids (ILs) for preconcentration of carbaryl and carbofuran in water samples is introduced. In this method, a small amount of sodium hexafluorophosphate (NaPF6), as an ion pairing agent, was added to a sample solution containing a small quantity of 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF4] as a hydrophobic ionic liquid. A cloudy solution formed as a result of formation of fine droplets of 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF 6]. After centrifugation, the fine droplets of the extractant phase settled to the bottom of the conical-bottom... 

It has been shown that one kind of poly silicon particles with sizes ranging from 10-500 nm, can be used in oilfields to enhance the oil recovery of water injection by 15-20%. The contributing mechanism might be reducing the interfacial tension which appears through improving relative permeability of the oil-phase. However, fundamental understanding of how hysteretic behavior of relative permeability curves affected by nanosilica particles remains a topic of debate in the literature. In this study, water as well as water dispersed nanosilica particles floods was performed on sandstone rock sample saturated by light crude oil supplied from one of Iranian oil reservoir, and the relative... 

It has been shown that one kind of poly silicon particles with sizes ranging from 10-500 nm, can be used in oilfields to enhance the oil recovery of water injection by 15-20%. The contributing mechanism might be reducing the interfacial tension which appears through improving relative permeability of the oil-phase. However, fundamental understanding of how hysteretic behavior of relative permeability curves affected by nanosilica particles remains a topic of debate in the literature. In this study, water as well as water dispersed nanosilica particles floods was performed on sandstone rock sample saturated by light crude oil supplied from one of Iranian oil reservoir, and the relative... 

This is the first research on the thermal buckling analysis of graphene nanoplatelets reinforced composite (GPLRC) doubly curved open cylindrical micropanel in the framework of numerical-based two-dimensional generalized differential quadrature method (2D-GDQM). Additionally, the small-scale effects are analyzed based on nonlocal strain gradient theory (NSGT). The stresses and strains are obtained using the high-order shear deformable theory (HOSDT). The rule of mixture is employed to obtain varying thermal expansion, and Poisson's ratio, while module of elasticity is computed by modified Halpin-Tsai model. In addition, nonlinear temperature changes along the GPLRC micropanel's thickness... 

To address the issue of cost and instability in perovskite solar cells (PSCs), it is promising to substitute the regular hole collecting electrode i.e., spiro-OMeTAD/Au with inorganic hole transport layer (HTL)/carbon electrode. In this study, three carbon pastes were investigated with different binders: polymethyl methacrylate (PMMA), styrene-butadiene-styrene (SBS) and ethyl cellulose (EC). Carbon layers were compared in terms of mechanical stability, conductivity and performance as back contact electrodes in PSCs with an inorganic HTM composed of CuInS2 nanoparticles. To assess mechanical properties of the carbon pastes, adhesion tests by using tape, ultrasonication in the media of... 

In this paper an analytical approach to study the effect of the substrate physical properties on the kinetics of adhesion and motility behavior of cells is presented. Cell adhesion is mediated by the binding of cell wall receptors and substrate's complementary ligands, and tight adhesion is accomplished by the recruitment of the cell wall binders to the adhesion zone. The binders' movement is modeled as their axisymmetric diffusion in the fluid-like cell membrane. In order to preserve the thermodynamic consistency, the energy balance for the cell-substrate interaction is imposed on the diffusion equation. Solving the axisymmetric diffusion-energy balance coupled equations, it turns out that... 

The governing equations of optical fiber Raman amplifier with broadband pumps in the steady state are systems of uncountable nonlinear ordinary differential equations (NODE). In this paper, the Moment method is used to reduce the uncountable system of NODE to a system of finite number of NODE. This system of equations is solved numerically. The results are compared with that of the full numerical method. It was shown that the Moment method is a precise and efficient technique for analysis of optical fiber Raman amplifier with broadband pumps. © 2007 Elsevier B.V. All rights reserved  

Oxidative stress has been implicated in the progression of age-related macular degeneration (AMD). Treatment with antioxidants seems to delay progression of AMD. In this study, we suggested an antioxidant delivery system based on redox-sensitive liposome composed of phospholipids and a diselenide centered alkyl chain. Dynamic light scattering assessment indicated that the liposomes had an average size of 140 nm with a polydispersity index below 0.2. The percentage of encapsulation efficiency of the liposomes was calculated by high-performance liquid chromatography. The carriers were loaded with N-acetyl cysteine as a model antioxidant drug. We demonstrated responsiveness of the nanocarrier... 

The main contribution of this paper is to present a new set of approximate analytical solutions for the parameters of a photovoltaic (PV) five-parameter double-diode model that can be used as initial values for the numerical solutions based on the Newton-Raphson method. The proposed formulations are developed based on only the limited information given by the PV manufacturers, i.e., the open-circuit voltage (V), the short circuit current (I), and the current and voltage at the maximum power point (Im). Compared with the existing techniques that require the entire experimental I-V curve or additional information such as the slope of the I-V curves of the open circuit and the short circuit... 

Production from gas condensate reservoirs requires precise determination of reservoir fluid properties along with their positive impact on real reservoir performance evaluation and fluid in place volume calculation. This fact is particularly important because liquid drop out phenomena occurs as a result of pressure drop due to fluid production and condensate remains in reservoir [Mohebzadeh, 2005. In this study the challenges and problems of fluid phase behavior simulation in southern Iranian retrograde gas condensate reservoirs is discussed. Most of the problems and challenges are inaccuracy of equation of states near the critical point, special conditions and produced fluid flow... 

This is the first research on the vibration and buckling analysis of a graphene nanoplatelet composite (GPLRC) microdisk in the framework of a numerical based generalized differential quadrature method (GDQM). The stresses and strains are obtained using the higher-order shear deformable theory (HOSDT). Rule of the mixture is employed to obtain varying mass density, thermal expansion, and Poisson's ratio, while the module of elasticity is computed by modified Halpin-Tsai model. Governing equations and boundary conditions of the GPLRC microdisk are obtained by implementing Extended Hamilton's principle. The results show that outer to inner ratios of the radius (Ro/Ri), ratios of length scale... 

The gain graphs are essential generalizations of the signed graphs. They are indeed directed graphs whose edges are labeled by the elements of a group rather than just ±1. In this paper, we prove the existence of matroids arising from these graphs. Further, we study the structure of the obtained matroids as well as their relation with the generalized Hamming weights, the regularity of the ideal of circuits, and the codes. © 2023 Elsevier B.V  

Background: Basic epidemiological data can provide estimates when discussing disease burden and in the planning and provision of healthcare strategies. There is little quantitative information in the literature regarding prevalence of traumatic injuries from developing countries. Objectives: The aim of the current preliminary study was to reveal the prevalence and age and gender distribution of various traumatic injuries in a tertiary referral orthopedic hospital in Iran. Patients and Methods: In a prospective descriptive study, all traumatic injured patients attending the Orthopedic Trauma Unit of our center in a five year period were included. Demographic details, the cause of injury,... 

A novel superabsorbent composite based on kappa-Carrageenan (κC) was prepared by graft copolymerization of acrylamide (AAm) onto κC in the presence of bentonite powder using methylenebisacrylamide (MBA) as a crosslinking agent, ammonium persulfate (APS) as an initiator, and sodium carbonate as a pore-forming agent. The swelling behavior in distilled water and in solutions with different pH values was investigated. The results indicated that with increasing carrageenan/bentonite weight ratio, the swelling capacity is increased but the gel content is decreased. The swelling rate of the hydrogels was improved by introducing sodium carbonate as pore-forming agent. The prepared superadsorbent... 

Parameter extraction of the five-parameter single-diode model of solar cells and modules from experimental data is a challenging problem. These parameters are evaluated from a set of nonlinear equations that cannot be solved analytically. On the other hand, a numerical solution of such equations needs a suitable initial guess to converge to a solution. This paper presents a new set of approximate analytical solutions for the parameters of a five-parameter single-diode model of photovoltaic (PV) cells and modules. The proposed solutions provide a good initial point which guarantees numerical analysis convergence. The proposed technique needs only a few data from the PV current-voltage... 

Certain physical and mechanical phenomena within ultra-thin face-centered cubic (fcc) films containing common types of interacting point defects are addressed. An atomic-scale lattice statics in conjunction with many-body interatomic potentials suitable for binary systems is conducted to analyze the effects of the depth on the: (1) formation energy and layer-by-layer displacements due to the presence of vacancy-octahedral self-interstitial atom (OSIA) ensemble, and (2) elastic fields as well as the free surface shape in the case of vacancy-dopant interaction. Moreover, the effects of the inter-defect spacing for various depths are also examined. To ensure reasonable accuracy and numerical...