Sharif Digital Repository

This paper concerns the design of a neural state observer for nonlinear dynamic systems with noisy measurement channels and in the presence of small model errors. The proposed observer consists of three feedforward neural parts, two of which are MLP universal approximators, which are being trained off-line and the last one being a Linearly Parameterized Neural Network (LPNN), which is being updated on-line. The off-line trained parts are able to generate state estimations instantly and almost accurately, if there are not catastrophic errors in the mathematical model used. The contribution of the on-line adapting part is to compensate the remainder estimation error due to uncertain parameters... 

This paper deals with the problem of optimal large-angle single-axis maneuvers of a flexible spacecraft with simultaneous vibration suppression of elastic modes. A spacecraft model with a cylindrical hub and one flexible appendage and tip mass is considered. Gravity gradient torque is considered as a disturbance torque. Multilayer perceptron neural networks are used to design a Neural Optimal Controller (NOC) for this multivariable non-linear maneuver. For NOC training, an off-line training procedure based on backpropagation through time algorithm is developed to minimize the general quadratic cost function in forward and backward pass stages. The proposed controller is also applicable to... 

A deterministic model for human immunodeficiency virus (denoted HIV) infection in the presence of combination therapy is considered. Global asymptotic stability of the disease-free equilibrium is discussed and the endemic equilibrium is also investigated. © 2006 Elsevier Ltd. All rights reserved  

Mobile Ad Hoc Networks (MANETs) are networks with selforganizing capabilities and without a fixed infrastructure. Wireless nodes communicate among themselves using multi-hop radio relaying, without requiring the packets to pass through a central access point or a base station. In a highly mobile and infrastructure-less scenario, pre-configuration of addresses is not possible. Therefore node addresses need to be configured dynamically with minimum delay and packet loss. Existing solutions for IP address auto-configuration do not address security issues. In this paper we propose a secure address autoconfiguration for Mobile Ad hoc Networks (MANET) based on Virtual Address Space Mapping [1].... 

The regular number of a graph (Formula presented.) denoted by (Formula presented.) is the minimum number of subsets into which the edge set of (Formula presented.) can be partitioned so that the subgraph induced by each subset is regular. In this work we answer to the problem posed as an open problem in Ganesan et al. (J Discrete Math Sci Cryptogr 15(2-3):49-157, 2012) about the complexity of determining the regular number of graphs. We show that computation of the regular number for connected bipartite graphs is NP-hard. Furthermore, we show that, determining whether (Formula presented.) for a given connected (Formula presented.)-colorable graph (Formula presented.) is NP-complete. Also, we... 

A proper labeling of a graph is an assignment of integers to some elements of a graph, which may be the vertices, the edges, or both of them, such that we obtain a proper vertex coloring via the labeling subject to some conditions. The problem of proper labeling offers many variants and received a great interest during recent years. We consider the algorithmic complexity of some variants of the proper labeling problems, we present some polynomial time algorithms and NP-completeness results for them  

A Not-All-Equal decomposition of a graph G is a decomposition of the vertices of G into two parts such that each vertex in G has at least one neighbor in each part. Also, a 1-in-Degree decomposition of a graph G is a decomposition of the vertices of G into two parts A and B such that each vertex in the graph G has exactly one neighbor in part A. Among our results, we show that for a given graph G, if G does not have any cycle of length congruent to 2 mod 4, then there is a polynomial time algorithm to decide whether G has a 1-in-Degree decomposition. In sharp contrast, we prove that for every r, r≥ 3 , for a given r-regular bipartite graph G determining whether G has a 1-in-Degree... 

In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quad- rupole sources of aerodynamic noise... 

Injection molding is one of the most important manufacturing processes for mass production of complex plastic parts. In this study, mold filling is simulated by using the OpenFOAM software for Non- isothermal Newtonian fluid. The OpenFOAM is an open source software that is used in Computational Fluid Dynamics (CFD) tools. The studied mold shape has a rectangular structure with a gate for Newtonian fluid injection. The simulation carried out at non-isothermal conditions and two-dimensional flow is considered. The velocity, shear stress and temperature changes in different parts of the mold are critically studied. We show that vortex formation plays an important role on changes of shear stress... 

In this research, the employment of an innovative but simple and cost effective method for turbulent reduction in a low speed wind tunnel is investigated and the effect of this turbulence reduction on the Power Spectrum and FFT-Based signals that obtained from Hot-wire Anemometry is studied. These terms represents the amount of power contained in the signals. Several situations are studied in this paper. One of these situations is when there are four screens in the settling chamber of the wind tunnel and after that by adding the trip strip in the contraction region of the wind tunnel the tests were repeated. In the next stage, three screens were removed from the settling chamber of the wind... 

Porous medium characteristics (e.g., pore geometry and medium heterogeneity) as well as the chemical nature of the co-solvents crucially affect the oil displacement efficiency during solvent flooding processes. In this work, initially saturated models with heavy crude oil were used to perform a series of solvent injection experiments. Several onequarter five-spot micromodels with pre-designed pore geometry were constructed and used. In addition, rock-look-alike flow patterns generated from thin sections of sandstone and dolomite reservoir rocks were etched onto glass plates to form micromodels mimicking the pore geometry and heterogeneity of these rocks. Four different groups of chemicals... 

The main issue in heavy oils enhanced recovery methods is to reduce their viscosity in order to get a better mobility. This is commonly obtained by blending the oil with light hydrocarbons. Co-solvents are good candidates to improve the hydrocarbon recovery efficiency especially in miscible processes. However, the effect of co-solvents on miscible flooding of heavy oil reservoirs at different pore geometries is not well understood. In this work different one-quarter five-spot network patterns along with those generated from reservoir rocks' thin sections were etches on glass surfaces. The models that had been initially saturated with the heavy crude oil were used to perform a series of... 

Nano-sized particles of manganese oxides have been prepared by a very simple and cheap process using a decomposing aqueous solution of manganese nitrate at 100 °C. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectrometry have been used to characterize the phase and the morphology of the manganese oxide. The nano-sized manganese oxide shows efficient catalytic activity toward water oxidation and the epoxidation of olefins in the presence of cerium(iv) ammonium nitrate and hydrogen peroxide, respectively  

Incorporation of calcium(ii), zinc(ii) and aluminium(iii) to manganese oxides greatly improved the activity of manganese oxide towards the epoxidation of olefins in the presence of anhydrous tert-butyl hydroperoxide as an oxidant  

Almost all of the heavy oil reservoirs contain discontinuous permeability barriers (shales) with different structures. However, the effect of shaly layer geometrical characteristics including: spacing from wells, discontinuity, orientation, shaly layers' spacing and length, and heterogeneous distribution on oil recovery factor in the presence of gravity force are not well understood. In this work, a series of solvent injection experiments were conducted on various vertical one-quarter five-spot glass micromodels, containing barriers, which were initially saturated with a heavy oil sample. The oil recovery was measured by analysis of the pictures provided continuously during the injection... 

Despite numerous experimental studies, there is a lack of fundamental understanding on how the chemical composition of a co-solvent at different wettability conditions might affect the pore-scale events and oil recovery efficiency in 5-spot models. In this study visualization of solvent injection experiments performed on a one-quarter five spot glass micromodel, which was initially saturated with the crude oil. One hydrocarbon solvent was considered as base, and four other groups of commercial chemicals, as well as their mixtures, were used as co-solvents. Microscopic and macroscopic displacement efficiency of solvent mixtures in both strongly water-wet and oil-wet media has been studied. It... 

Despite the fact that control charts are able to trigger a signal when a process has changed, it does not indicate when the process change has begun. The time difference between the changing point and a signal of a control chart could cause confusions on the sources of the problems. Knowing the exact time of a process change would help to reduce the time for identification of the special cause. In this article, a model for the change-point problem is first introduced and a maximum-likelihood estimator (MLE) is applied when a linear trend disturbance is present. Then, Monte Carlo simulation is applied in order to evaluate the accuracy and the precision performances of the proposed...