Sharif Digital Repository

In this paper, an endochronic constitutive model is developed for cold powder compaction processes. As large deformations are observed in powder forming processes, the endochronic constitutive model based on large strain plasticity is presented and an integration scheme for the rate constitutive equations is established. Although the concept of yield surface has not been explicitly assumed in the endochronic theory, it is demonstrated that the cone-cap yield surface can be derived as a special case of the proposed endochronic model. The plastic flow rule and the dilatancy condition of the model are derived and a procedure for calibration of material parameters of the constitutive model is... 

This article presents a method for fast fault injection into switch-level circuits using FPGA chips. In this method, gates model switch-level circuits and we can emulate mixed gate-switch-level models. By the use of this method, FPGA chips can be used to accelerate the fault-injection campaigns into switch-level models. The approach has been evaluated experimentally by injecting a set of faults into a pipelined RISC processor. The experimental results show that significant speed-ups with respect to fully simulation-based fault-injection methods can be achieved. © 2004 Elsevier B.V. All rights reserved  

Asphaltene precipitation and deposition is one of the main problems in some of the oil fields. The deposited asphaltene results in partial or total blockage of the wellstring and reducing or completely seizing oil production. Asphaltene deposition problems have been experienced in the field for a long time. Although, the asphaltene precipitation has been studied thoroughly and different parameters that effects this process has been investigated but little work has been carried out in the asphaltene deposition across the production system of flowing oil well. This paper introduces a new comprehensive model for description of asphaltene deposition behavior in wellstring. The mechanisms of... 

This paper presents a method for the fast emulation of switch-level circuits using FPGAs. In this method, logic gates are used to model switch-level circuits without any abstraction. In contrast to the abstraction methods for which transistors are grouped together to form gates, in this method, gates are grouped together to form the switch models of transistors. Unlike the abstraction methods, the method presented in this paper can emulate many important features of switch-level models, such as bi-directional signal propagation and variations in driving strength. In order to attain a better utilization of FPGA resources a mixed-mode emulation approach has been used. In this approach parts of... 

Excess enthalpy data measured at 298.15 K were collected from the literature. The data contains 48 binary systems (812 data points). The experimental data were correlated by the Redlich-Kister equation. In this research work the following thermodynamics models were also tested, Wilson, NRTL models and their parameters were calculated. A modified NRTL with composition-dependent (α12) parameter were also proposed. The correlation of excess enthalpy data in the systems using this model provides good results  

This paper presents nonlinear signal and noise analysis of a wide gate FET mixer. The study is performed using nonlinear sliced modeling. The FET is taken into account as a distributed element and divided into several smaller pieces so that in each slice a lumped model can be applied. Calculation of passive and active elements of each slice is performed using proper scaling approach. For noise analysis, appropriate noise sources are added to the distributed circuit The wide gate FETs have been suggested for high power, wideband and high gain devices such as travelling wave amplifier. The nonlinear application is suggested for a novel device named travelling wave mixer. © 2000 IEEE  

Special attention is given to vertical takeoff and landing air vehicles due to their unique capabilities and versatile missions. The main problem here is control effectiveness at low flight speeds and transition maneuvers because of the inherent instability. RMIT is a small sized tail-sitter ducted fan air vehicle with a particular configuration layout, multiple control surfaces, low weight, and high-speed flight capability. In the current study, a comprehensive nonlinear model is firstly developed for RMIT, followed by a validation process. This model consists of all parts including aerodynamic forces and moments, control surfaces term together with the gravity and driving fan forces.... 

One of the most promising methods for transporting natural gas and overcoming its low energy density is adsorbed natural gas (ANG) technology. ANG technology is highly dependent on the perfect conception of adsorption isotherms in different operational conditions and on different adsorbents. In this study, the utilization of a novel mathematical model of least squares support vector machine (LSSVM) for accurate prediction of adsorption isotherm has been examined. The considered variables were temperature, pressure and type of adsorbents. A data set containing 670 experimental data points of methane adsorption on 10 different adsorbents in a broad range of temperature and pressure were used... 

A one-dimensional kinetic Ising model at a finite temperature on a semi-infinite lattice with time varying boundary spins is considered. Exact expressions for the expectation values of the spin at each site are obtained, in terms of the time dependent boundary condition and the initial conditions. The solution consists of a transient part which is due to the initial conditions, and a part driven by the boundary. The latter is an evanescent wave when the boundary spin is oscillating harmonically. Low-and high-frequency limits are investigated in greater detail. The total magnetization of the lattice is also obtained. It is seen that for any arbitrary rapidly varying boundary conditions, this... 

We investigate a new version of sandpile model which is very similar to Abelian Sandpile Model (ASM), but the height variables are continuous ones. With the toppling rule we define in our model, we show that the model can be mapped to ASM, so the general properties of the two models are identical. Yet the new model allows us to investigate some problems such as the effect of very small mass on the height probabilities, different boundary conditions  

Lander-Waterman's coverage bound establishes the total number of reads required to cover the whole genome of size G bases. In fact, their bound is a direct consequence of the well-known solution to the coupon collector's problem which proves that for such genome, the total number of bases to be sequenced should be O(G ln G). Although the result leads to a tight bound, it is based on a tacit assumption that the set of reads are first collected through a sequencing process and then are processed through a computation process, i.e., there are two different machines: one for sequencing and one for processing. In this paper, we present a significant improvement compared to Lander-Waterman's... 

Ship transportation is increasing globally as is the risk of collision especially in congested areas. Numerical modeling method is a major simulation method to predict ship maneuverability. Ship maneuvering in calm water is an important topic to avoid collisions and leads to safe navigation. Therefore, reliable ship maneuvering simulations are required for incident analysis and prevention. In recent time within the research community orientated towards ship hydrodynamics an increasing attention has been paid to simultaneous solution of the planing ship maneuvering problem. The maneuverability of planing craft has been the subject of many research projects during the last few decades. To... 

In this research a mathematical model for controlled drug delivery of Ibuprofen has been developed which accounts for physical kinetics based upon variations of the drug concentration, size and release time for a spherical drug pill. Through this model, the drug release for three sizes of the active ingredient including; 213nm (representing existence of only diffusion limitations), 515nm (representing existence of only solubility limitations) and 367nm (representing both diffusion and solubility limitations) was calculated. Theoretical amounts of the drug after two hours of release are calculated to be 95.3, 99.5 and 95.5 percent, respectively. Comparison of theoretical and experimental data... 

The one-dimensional anisotropic Kondo-necklace model has been studied by several methods. It is shown that a mean field approach fails to gain the correct phase diagram for the Ising-type anisotropy. We then applied the spin wave theory which is justified for the anisotropic case. We have derived the phase diagram between the antiferromagnetic long range order and the Kondo singlet phases. We have found that the exchange interaction (J) between the itinerant spins and local ones enhances the quantum fluctuations around the classical long range antiferromagnetic order and finally destroy the ordered phase at the critical value Jc. Moreover, our results show that the onset of anisotropy in the... 

In this work, the modified Wilson model was used to obtain the activity coefficients of amino acids and simple peptides in non-electrolyte aqueous solutions. The Wilson model was modified using the new local mole fraction proposed by Zhao et al. and non-random case for the reference state. The binary interaction parameters (BIP) of the modified Wilson model for amino acid-water pairs were obtained using the experimental data of the activity coefficients for amino acids available in the literature. The modified Wilson model was also used to correlate the solubility of amino acids in water and the values of Δh/R, Δs/R, and Δg/R of the solutions studied were reported. The results obtained... 

We present in this paper a new method of modifying hard-core potentials to correctly predict the equilibrium and non-equilibrium properties of real fluids at low densities (specifically when ρ ≤ B/C where ρ is density, and B and C are the second and third virial coefficients) only by one set of potential parameters. Because the molecular diameter becomes smaller when temperature increases, we introduced a new expression for the variation of molecular diameter with temperature that incorporates this effect. The temperature dependence of the diameter was used in both Sutherland (ST) and square-well (SW) potential models to modify the second virial coefficient. Then we have shown that the... 

Safe and efficient pedestrian movement is an important issue of concern in traffic engineering. Evaluation and identification of effective parameters in pedestrians' decision-making process when crossing a street can be beneficial in improving their safety. In this report, two streets in Tehran, Iran were selected to study the pedestrians' crossing. The data from the video films at these locations were used to fit the logit and nested logit models. The results indicate that factors such as arrival time of first nearside vehicle to crosswalk, headway between first and second vehicle approaching the crosswalk, vehicles platoon size and their approaching speed in each lane, pedestrians' age,... 

We present axiom systems, and provide soundness and strong completeness theorems, for classes of Kripke models with restricted extension rules among the node structures of the model. As examples we present an axiom system for the class of cofinal extension Kripke models, and an axiom system for the class of end-extension Kripke models. We also show that Heyting arithmetic (HA) is strongly complete for its class of end-extension models. Cofinal extension models of HA are models of Peano arithmetic (PA). © 2003 Elsevier B.V. All rights reserved  

Several corrosion inhibitors, such as, HEDP, sodium molybdate and zinc ions, were added to an aqueous corrosive media containing different concentrations chloride ions, and the corrosion rates (CRs) of carbon steel were measured at various temperatures. It was shown that, in the presence of more than 1,200 ppm of chloride ions, and temperatures greater than or equal to 42.5°C, the combination of HEDP, molybdate and zinc could not control the corrosion in a cooling water system. Then four different models were designed to represent the CR of carbon steel in presence of various corrosive parameters