فهرست مطالب

Science and Technology Transactions of Electrical Engineering - Volume:38 Issue: 1, 2014

Iranian Journal of Science and Technology Transactions of Electrical Engineering
Volume:38 Issue: 1, 2014

  • تاریخ انتشار: 1393/03/17
  • تعداد عناوین: 7
|
  • M. Khalighi, B. Vosoughi Vahdat, M. Mortazavi, M. Mikaeili Pages 1-20
    Electrical Impedance Tomography (EIT), is one of the safest medical imaging technologies and can be used in industrial process monitoring. In this method, image of electrical conductivity (or electrical impedance) distribution of the inner part of a conductive subject can be reconstructed. The image reconstruction process is done by injecting an accurate current into the boundary of a volume conductor (Ω), measuring voltages around the boundary (∂Ω) and transmitting them to a computer, and processing on acquired data with software (e.g. MATLAB).The image would be reconstructed from the measured peripheral data by using an iterative algorithm. A precise instrumentation (EIT hardware) plays a very important and vital role in the quality of reconstructed images. In this paper, we have proposed a practical design of a low-cost precise EIT hardware including, a high output impedance VCCS (Voltage-Controlled Current Source) with pulse generation part, precise voltage demodulator and measuring parts, a high performance multiplexer module, and a control unit. All the parts have been practically and accurately tested with successful results, and finally the proposed design was assembled on PCB. The quality of experimental results at the end of this paper, (reconstructed images by using the implemented system), confirms the accuracy of the proposed EIT hardware.
    Keywords: EIT, electrical impedance tomography, EIT hardware, EIT instrumentation, EIT current source
  • S. Samadi, B. Zakeri, M. Zahabi Pages 21-32
    This paper analyzes the phase noise of the single loop second-order frequency fractional-N synthesizer. The aim of this paper is the reduction of the output phase noise in the application of commercial and military subsystems as well as general local oscillators. The mathematical model of PLL based frequency synthesizer is analyzed to develop the minimum phase noise in the specific frequency range. An exact closed form relationship between bandwidth and output phase noise of the frequency synthesizer as well as the bandwidth-phase noise diagram is extracted by using this closed form relationship. From the analysis and simulation results, we observe that the system has minimum phase noise at a particular closed-loop bandwidth. To validate simulation results, the synthesizer is implemented on the low loss professional printed circuit board (PCB). Measurement setup is scheduled on spectrum analyzer 8562A in the span of 5MHz and 10MHz. These measurements show excellent results in output spectrum of the frequency synthesizer.
    Keywords: Frequency synthesizers, phase noise, phase, locked loop, phase noise reduction
  • A. Rahideh, H. Moghbelli, T. Korakianitis Pages 33-57
    This paper investigates a 2-dimensional (2-D) analytical magnetic field prediction for doubly-salient machines. Using the subdomain technique, the effects of saliency on both the rotor and stator structures as well as their interactions are considered. The approach can be used for magnetic field calculation in machines with any combination of rotor- and stator-pole number. Three different stator winding structures are considered: non-overlapping winding with all teeth wound, non-overlapping winding with alternate teeth wound and 2-layer overlapping winding. To enable the analytical solution of the governing partial differential equations, the stator and rotor iron is assumed to be infinitely permeable and therefore the saturation effects are neglected. The proposed approach is used in two case studies: (1) to calculate the armature reaction magnetic field distribution of a three-phase slotted brushless machine with surface inset magnets and 2) to compute the magnetic field distribution of a four-phase switched reluctance motor. Note that the proposed approach cannot be employed in the case of machines with considerable saturation effects. The analytical results are compared with those obtained from finite element analyses to validate the analytical calculations.
    Keywords: Subdomain, brushless machines, switched reluctance machine, surface inset magnet
  • S. M. Fakhrahmad*, A. R. Rezapour, M. Zolghadri Jahromi, M. H. Sadreddini Pages 59-72
    Compared to corpora-based machine translation methods, rule-based methods have deficiencies, which make them unattractive for the researchers of this field. The first problem is that these methods are language dependent. Rule-based methods require the syntactic information about source and target languages. On the other hand, in many cases, especially for proverbs and specific expressions, syntactic rules are not useful anymore. In such cases, the use of examplebased approaches is inevitable. In this work, we propose and integrate a set of novel schemes to introduce a new translation system, called BORNA. First a grammar induction method based on the Expectation Maximization (EM) algorithm is proposed. After representing the extracted knowledge in the form of a set of nested finite automata, a recursive model is proposed, which uses a combination of rule and example based techniques. In the translation phase, through a hierarchical chunking process, the input sentence is divided into a set of phrases. Each phrase is searched in the corpus of examples. If the phrase is found, it will not be chunked anymore.Otherwise, the phrase is divided into smaller sub-phrases. The simulation results show that BORNA outperforms its counterparts, significantly. Compared to PARS, Frengly and Google translators, BORNA receives the highest Bleu scores for its translations, while it results in the minimum values for different error measures, including PER, TER and WER.
    Keywords: Machine translation, example, based, rule, based, corpora, based, finite automata, grammar induction
  • S. Kardani, Moghaddam, R. Entezari, Maleki, A. Movaghar Pages 73-90
    This paper investigates the scheduling problem of independent tasks in market-based grids. The heterogeneity and autonomy of resources in grids highlight the need for more flexible models and approaches to be exploited in these environments. To address this issue, a two-level market model is presented in this paper to schedule tasks to the grid resources. In the proposed model, users submit their own tasks to a centralized resource manager named meta scheduler. Meta-scheduler knows general information about each of the administrative domains, called sites, existing in the low-level part of the model. Using the information gathered from all of the sites, meta-scheduler selects more suitable sites to execute the tasks with the aim of minimizing the overall cost of tasks execution. In this model, meta-scheduler not only targets the minimization of overall cost of the tasks execution, but also achieves this objective without any presumption about the policies and algorithms implemented in the lower layers of the system which addresses the dynamicity of environment. In addition to the two-level market model, a new task scheduling algorithm called GA-VNS which is an enhanced version of genetic algorithm is presented to be applied in market-based grids. GA-VNS can be used by local schedulers in each site with the policy of cost minimization considering the makespan of the system as a second criterion. The results obtained from performance evaluation of GA-VNS and other well-known algorithms in this context show that GA-VNS outperforms other algorithms in terms of the overall cost of tasks execution.
    Keywords: Grid environment, scheduling algorithm, local search, execution cost, task deadline
  • S. Khorshidi Pages 91-97
    Reverberation noise in active sonar leads to a very complicated situation for target detection. Reverberation is often modeled as the autoregressive model. In this paper, the autoregressive model is considered for reverberation and the Principal Component Inverse (PCI) algorithm is used to separate target echo signal from reverberation. This consideration helps us to propose a new method to improve computational complexity for the rank determination of the observation matrix via singular value decomposition. It is shown that this new method is efficient on real data to separate target echo signal from reverberation.
    Keywords: Reverberation cancellation, autoregressive model, principal component inverse (PCI) algorithm
  • H. Zhang, Z. Shou, J. Zhang, Q. He, J. Qian Pages 99-109
    Service reputation is a key factor for service selection and service composition in Service-Oriented Ambient Intelligence systems. Hence, service reputation computing should fully reflect the feature of multi-rating fusion and the utility value dynamic attenuation characters of the rating. The paper combines D-S evidence theory with dynamic attenuation and puts forward a service reputation computing algorithm based on multi-rating fusion, which is adapted to the Ambient Intelligence systems. First, a layered computing model of the service reputation is given. Then, a mechanism of dynamic attenuation based on time windows, an objective rating and advertisement honesty rating of service, and a user credibility computing algorithm are presented. Afterward, the rating information is combined with the D-S evidence theory to raise an aggregation algorithm of the service general reputation for the Ambient Intelligence environments. Finally, a prototype test is carried out to verify the effectiveness and availability of the model together with the algorithms.
    Keywords: Service reputation, trust, evidence theory, AmI