Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Introducing a New Definition Towards Clinical Detection of Microvascular Changes Using Diffusion and Perfusion MRI
2462
EN
M.
Ashoor
Department of Mechanical Engineering,Sharif University of Technology
Journal Article
2006
04
04
Based on MRI diffusion and perfusion, a new criterion for detection and the healing progress of damaged tissue is suggested. The study is based on the ratio of capillary radii in symmetrical damaged and normal tissue neighboring spaces. The Apparent Diffusion Coefficient (ADC) and Cerebral Blood Flow (CBF) were measured in the brain tissues of six male Wistar rats utilizing suggested MRI measurement techniques. The ADC values of damaged and normal regions were (392pm34.1)times10^{-6} mm^2s^{-1} and (659pm40.7)times10^{-6} mm^2s^{-1}, respectively. The CBF values of damaged and normal regions were 14.5pm10.13 ml/min/100 g and 125pm41.03 ml/min/100 g, respectively. The geometrical parameters of the capillary for damaged and normal regions, overline{r}/sqrt{overline{l}}, where overline{r} is the mean radius and overline{l} is the mean capillary segment length, were calculated to be 5.45pm2.01 mm^{0.5}g^{-0.5} (mean pm SD) and 12.8pm2.04 mm^{0.5}g^{-0.5}, respectively. Furthermore, based on constant overline{l}, the damaged, versus normal region, mean radius, was shown to follow the ``criterion'': overline{r}_{Damaged}cong0.43timesoverline{r}_{Normal}. A further analysis was conducted through suitable theoretical modeling and assumptions for the above-mentioned criterion. The analysis showed a distinct difference between normal and damaged tissues in various healing progress conditions. Moreover, a new image, namely, Diffusion/Flow map (DF map), which is a mere division of the ADC map to the CBF map, was introduced and utilized to contrast between normal and damaged tissue.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
On a Theorem of Ihara
2463
EN
A.
Rastegar
Department of Mathematics,Sharif University of Technology
Journal Article
2006
04
04
Let p be a prime number and let n be a positive integer prime to p. By an Ihara-result, one means the existence of an injection with torsion-free cokernel, from a full lattice, in the space of p-old modular forms, into a full lattice, in the space of all modular forms of level np. In this paper, Ihara-results are proven for genus two Siegel modular forms, Siegel-Jacobi forms and Hilbert modular forms. Ihara did the genus one case of elliptic modular forms [1]. A geometric formulation is proposed for the notion of
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Regular RGC_n-Commutative Semigroups
2464
EN
A.
Nagy
Department of Algebra,Budapest University of Technology & Econamics
Journal Article
2006
04
04
In this paper, it is proven that a semigroup is regular and RGC_n-commutative if, and only if, it is a spined product of a ommutative Clifford semigroup and a right regular band.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Stochastic Optimization Using Continuous Action-Set Learning Automata
2465
EN
H.
Beigy
Department of Civil Engineering,Sharif University of Technology
Journal Article
2006
04
04
In this paper, an adaptive random search method, based on ontinuous action-set learning automata, is studied for solving stochastic optimization problems in which only the noise-corrupted value of a function at any chosen point in the parameter space is available. First, a new continuous action-set learning automaton is introduced and its convergence properties are studied. Then, applications of this new continuous action-set learning automata to the minimization of a penalized Shubert function and pattern classification are presented.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Optimal Production and Maintenance Control Under a Time Variant Demand
2466
EN
F.
Kianfar
Department of Industrial Engineering,Sharif University of Technology
Journal Article
2006
04
04
In this paper, optimal production and maintenance planning of a flexible manufacturing system under a time variant demand is considered. There is a preventive maintenance plan to reduce the failure rate of the machine. It is assumed that the failure rate of the machine is a function of its age and its maintenance rate. It is, also, assumed that the demand of the manufacturing product is time dependent and its rate depends on the level of the advertisement on that product. The objective is to maximize the expected discounted total profit of the firm over an infinite time horizon. To solve this optimization problem, first, an optimal control is characterized by a set of Hamilton-Jacobi-Bellman partial differential equations. Then, since this set of equations cannot be solved analytically, this stochastic optimal control model is approximated by a deterministic optimal control problem. By solving this new deterministic problem under practical assumptions, a set of suboptimal controls can be found.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
An Approach to Volt/Var Control in Distribution Networks with Distributed Generation
2467
EN
T.
Niknam
Department of Electrical Engineering,Sharif University of Technology
Journal Article
2006
04
04
Due to deregulation and restructuring in many countries, it is expected that the amount of small-scale generations connected to the distribution networks will increase. So, it is necessary that the impact of these kinds of generators on Volt/Var control should be investigated. This paper presents a new approach to Volt/Var control in distribution systems with Distributed Generation (DG). It has been shown that DG can improve the entire performance of a network system, by means of better control and decreasing losses. In this approach, the Genetic Algorithm (GA) has been used as the optimization method, where the amount of DG and its controlling parameters, the voltage regulators situation, the status of the load tap changers and, finally, the amount of switched capacitor, have been assumed as state variables. This method is tested on IEEE 34 bus radial distribution test feeders and a rural distribution network. The results are presented and it is shown that in the case of the selection of a correct location for DG, the system losses can be decreased by up to 70%.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Analysis of the Convergence and Closed Loop Stability in EDMC
2468
EN
M.
Haeri
Department of Electrical Engineering,Sharif University of Technology
Journal Article
2006
04
04
In this paper, the convergence and stability conditions of extended DMC in the control of nonlinear SISO and MIMO systems are investigated. The formulations are based on the ordinary DMC in which, with successive linearization of the nonlinear model and new interpretation of disturbance, the nonlinear extension is deduced. In addition, new convergence and stability criteria are derived for SISO and MIMO systems. These criteria include convergence and stability in the case of longer control (M>1) and prediction (P>1) horizons, as well as the finite and infinite sampling time. Finally, the simulation results for a MIMO (3x3) model, based on a power unit nonlinear plant, are presented.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Integrating Model Checking and Deduction for Rebeca
2469
EN
M.
Sirjani
Department of Computer Engineering,Sharif University of Technology
Journal Article
2006
04
04
Rebeca is an actor-based language for modeling concurrent and distributed systems. Its Java-like syntax makes it easy-to-use for practitioners and its formal foundation is a basis to make different formal verification approaches applicable. Compositional verification and abstraction techniques are used in formal verification of Rebeca models to overcome state explosion problems. The main contribution of this paper is to show how model checking and deduction are integrated for verifying certain properties of these models. Deduction is used to prove that abstraction techniques preserve a set of behavioral specifications in temporal logic and is also used in applying the compositional
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Stability Analysis of a Second-Order Proportionally-Fair Rate Allocation Algorithm
2470
EN
P.
Goudarzi
Department of Electrical & Computer Engineering,Isfahan University of Technology
Journal Article
2006
04
04
In this paper, a delay-difference second-order proportionally-fair rate allocation algorithm has been proposed. As conventional proportionally-fair rate allocation algorithms deploy some form of scaled gradient ascent iterative algorithm for converging to user optimal rates, using fast second-order algorithms, such as Jacobi or approximate Newton methods, can be considered as natural and good candidates for increasing the convergence speed of the rate allocation algorithms. Stability analysis, related to scaled gradient ascent algorithms, in the presence of propagation delays, has been performed by some researchers, such as R. Johari et al., in Cambridge. In the current paper, the stability conditions of a second-order Jacobi method in the presence of propagation delays, with the simplifying premise of equality between all the users' propagation delays, is derived mathematically. Simulation results show that even in the general case of different propagation delays, stability is maintained.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Optimization of Higher Order Pulse Shapers Used for Reduction of Noise in Amplifier Circuits
2471
EN
M.
Tabandeh
Department of Electrical Engineering,Sharif University of Technology
Journal Article
2006
04
10
Active components in amplifiers generate noise. Thus, amplifiers too, produce noise at their output and, therefore, increase the input signal to noise ratio. This is an undesirable feature, more particularly when one is dealing with weak input signals already combined with noise. Thus, reducing amplifiers' noise becomes a necessity for some applications. To overcome this problem, one approach consists of improving electronic device technology. Another approach is the use of advanced techniques in designing low noise amplifiers by taking advantage of pulse shapers. Pulse shapers generally consist of calculated filters made of integrator(s) and differentiator(s) that limit properly the amplifier bandwidth and, thereby, limit noise through the amplifier. In this study, the effect of variations of parameters of a single differentiator dual integrator pulse shaper on the reduction of noise in an amplifier circuit is investigated and their corresponding values are found for an optimal design.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Biosignals: A General Approach for Analysis
2472
EN
K.
Niknam
Department of Electrical Engineering,Sharif University of Technology
Journal Article
2006
04
10
In this paper, a biosignal analysis approach to determine the relation between a typical cell action current (potential) and its resulted biosignals is presented. This relation is a logical result that can be obtained from the electrophysiological concepts governing the biosignals generating phenomena and can tell us some facts about its generating organ. Therefore, one has an input Action Current or AC), an output (biosignal) and an unknown system (black box) relating them together. In this study, a linear system modeling is proposed to identify that relationship. This system acts as a transfer function (or generating function) that generates different forms of biosignal from a unique input (AC) waveform and can describe the functional physiology of the generating tissue (as muscle, brain and etc.). This expression is useful in simulating biopotential signals and, also, in diagnosing their normality or abnormality. In special cases, this relationship and system identification methods for some typical ECGs are used to diagnose some arrhythmias by comparing their generating functions.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
A Genetic Algorithm for Resource Investment Problems, Enhanced by the Revised Akpan Method
2473
EN
F.
Kianfar
Department of Industrial Engineering,Sharif University of Technology
Journal Article
2006
04
10
In this paper, a genetic algorithm for solving a class of project scheduling problems, called Resource Investment Problems, is presented. Tardiness of the project is permitted with a defined penalty. The decision variables are the level of resources and the start times of the activities. The objective is to minimize the sum of resources and delay penalty costs, subject to the activities' precedence relations and some other constraints. A revised form of the Akpan heuristic method for this problem is used to find better chromosomes. Elements of the algorithm, such as chromosome structure, unfitness function, crossover, mutation, immigration and local search operations, are explained. The performance of this genetic algorithm is compared with that of other published algorithms for Resource Investment Problems. Also, more than 700 problems are solved using an enumerating algorithm and their optimal solutions are used for the performance tests of the genetic algorithm. The tests results are quite satisfactory.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Application of Artificial Neural Networks in Controlling Voltage and Reactive Power
2474
EN
R.
Hooshmand
Department of Electrical Engineering,Isfahan University of Technology
Journal Article
2006
04
10
This paper presents an application of Artificial Neural Networks (ANN) to control the voltage and reactive power in power systems. The technique is based on using a feed-forward artificial neural network with an error back-propagation training algorithm, based on the Levenberg-Marquardt method to train the networks. The training data is obtained by solving several abnormal conditions using Linear Programming (LP). Generator voltages, reactive power sources and transformer taps are considered as control variables and load bus voltages and generator reactive powers as dependent variables. The method presented in this paper has been tested on IEEE 14-bus and 30-bus standard systems. The obtained results clearly indicate that the trained neural networks are capable of controlling the voltage and reactive power in power systems with a high level of precision and speed.
Sharif University of Technology
Scientia Iranica
1026-3098
12
1
2005
01
01
Investigation into Some Parameters Affecting Pectin Gel Quality
2475
EN
I.
Alemzadeh
Department of Chemical and Petroleum Engineering,Sharif University of Technology
Journal Article
2007
05
01
In this research, gel production from the extracted pectin gel of shahroud sugar beet pulp has been investigated. The pectin extractions were performed in a cold alkaline solution and a hot acid solution, respectively. The effects of different parameters, such as percent of sugar, pectin concentration, calcium content and quantity of peroxidase enzyme, hardness and content of water absorbed by the gel, were studied. Optimum conditions for production of favorable gel, from extracted pectin in this research are, as follows: Percent of sugar (glucose): 15%, peroxidase enzyme content: (pectin unit) 170 pu/g of pectin, pectin concentration (if only gel water uptake is important): 10%, pectin content (if only strength and hardness of gel are important): 15%, calcium content (if only gel water uptake is important): 60 mg CaCl_2/g of pectin and calcium content (if only gel uptake strength is important): 80 mg CaCl_2/g of pectin. Simultaneous application of peroxidase enzyme and hydrogen peroxide as oxidizing agents, besides calcium, glucose and suitable content of LM (Low Methoxyl) pectin, resulted in interesting properties and a decrease in gel formation time from ``5 minutes - 24 hours'', to ``15 - 20 seconds'' and a favorable increase in gel strength.