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Volume 12, Issue 1, 2005
Electrical and Computer Engineering
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Introducing a New Definition Towards Clinical Detection of Microvascular Changes Using Diffusion and Perfusion MRI
M. Jahed (PhD.)
M. Ashoor [PhD.]
Q. Jiang [PhD.]
M. Chopp [PhD.]
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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 (392\pm34.1)\times10^{-6} mm^2s^{-1} and (659\pm40.7)\times10^{-6} mm^2s^{-1}, respectively. The CBF values of damaged and normal regions were 14.5\pm10.13 ml/min/100 g and 125\pm41.03 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 5.45\pm2.01 mm^{0.5}g^{-0.5} (mean \pm SD) and 12.8\pm2.04 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}\cong0.43\times\overline{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. |
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An Approach to Volt/Var Control in Distribution Networks with Distributed Generation
T. Niknam (PhD.)
A.M. Ranjbar [PhD.]
A.R. Shirani [PhD.]
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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%. |
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Stability Analysis of a Second-Order Proportionally-Fair Rate Allocation Algorithm
P. Goudarzi (PhD.)
F. Sheikholeslam [PhD.]
H. Saidi [PhD.]
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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. |
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Optimization of Higher Order Pulse Shapers Used for Reduction of Noise in Amplifier Circuits
M. Tabandeh (PhD.)
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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. |
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A Genetic Algorithm for Resource Investment Problems, Enhanced by the Revised Akpan Method
S. Shadrokh (PhD.)
F. Kianfar [PhD.]
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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. |
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Investigation into Some Parameters Affecting Pectin Gel Quality
I. Alemzadeh (PhD.)
B. Ebrahimi [PhD.]
S.K. Seifkordi [PhD.]
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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. |
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