IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2006 | Volume:30 | Issue:B2|Papers Count:12

Document clustering has been widely used in information retrieval systems in order to improve the efficiency and also the effectiveness of ranked output systems using clustering hypothesis. Based on this hypothesis, documents relevant to a query tend to be highly similar in the context defined by the query. In this way, a pair of documents has an overall similarity (ignoring the query) and a specific similarity (similarity of a pair of documents given a query). A Query-Sensitive Similarity Measure (QSSM) is a mechanism to measure the similarity of two documents given a query. In this paper, in the first step, we identify the sources of information that may be used for this purpose. In the second step, we propose a QSSM based on these information sources. Finally, we propose a parametric QSSM that simultaneously makes use of the product and weighted sum to fuse the information from the identified sources. A genetic algorithm is used to learn the optimal values of parameters in this measure for a specific collection. The leave-one-out method is used to evaluate the proposed learning scheme. Our motivation for this is to see whether the learning scheme can perform significantly better than the measure proposed in the second step. Using several document collections, the performance of each measure is evaluated and the results are compared with other QSSMs proposed in the past research.

This paper describes an architectural model to facilitate multiversion objects that are explicitly designed to enhance concurrency. The reader should be aware that version management has been used in the object literature in several ways, most commonly dealing with design issues. Our goal here is related to concurrency control and reliability, so care must be taken to ensure the reader is not misled by this overloading of terminology found in the literature. Within the context of concurrency the key aspects addressed by this paper are: 1) An architectural model is developed to support multiversioning that provides the well-known ACID transaction properties; 2) An optimistic concurrency control algorithm that functions on this architecture is described and demonstrated to be correct with respect to a correctness criterion; 3) The algorithm is enhanced to examine the history of past versions with the goal of inserting a committing transaction at a time earlier in the sequence when it would have been valid if other, later transactions had not been completed before this one attempted to commit; and 4) Based on static analysis information, other algorithms are developed to optimize the compiler in order to generate reconciliation procedures automatically from the initial transaction specification.

In the test of a circuit for faults it is very desirable to have the minimum paths that are to be tested for a complete circuit test. At first, the best test vectors are chosen and then these pairs of vectors are applied to the circuit. Each of these pair of vectors is able to detect a certain number of the faults and the path delay fault coverage for each and all of them may be calculated.Suitable choice of a path may result in the coverage of the whole circuit and increases detected faults. In this paper, a new method for choosing the minimum suitable paths is introduced. Decreasing the number of test paths causes an increase in the number of detectable faults by a certain number of test vector pairs, hence giving a better fault coverage. In the presented method, a test path would be selected, if and only if, there exists at least one "two-piece" segment in that path which has not been tested before in the previously tested paths. If the chosen path has at least one "three-piece" (or "more-piece") segment the method will become more complicated. The method is applied to some ISCAS89 benchmarks circuits.

Proportional fairness criterion, first proposed by Kelly, has outstanding properties in allocating fair rates to network users. For example, it resembles the Jacobson’s AIMD method in rate allocation to users, and there exists a well-established stability analysis relating to the stability of the rate allocation algorithm. Kelly’s algorithm uses a form of the scaled gradient ascent projection method for converging to the equilibrium point. The structure of Kelly’s algorithm is such that in some instants of time, the aggregate flow which is passing through a link may exceed the link capacity. In other words, the algorithm is not loss-free. In this paper, we have proposed a novel time-varying scaled gradient ascent projection method that, under some assumptions about the link penalty function, the rate allocation algorithm is loss-free in some network topologies. Also, it is shown by simulation that in a general network topology, the proposed algorithm does not have any loss event in comparison with the Kelly’s method.

For induction motor drives controlled by the indirect rotor flux oriented control (IRFOC), the rotor resistance variation results in an undesirable coupling between the flux and the torque of the machine, and loss of dynamic performance. This paper presents a scheme for the estimation of rotor resistance using a neural networks (NN) block. In this system the flux and torque have been estimated by using stator voltages and currents. A back-propagation NN receives the flux and torque errors and a supposed rotor resistance at the input and estimates the actual rotor resistance at the output, which is used in the control of an indirect vector-controlled drive system. The neural network has been trained off line with the mathematical model of the control scheme in detuning operations. IRFOC control, used with the NN estimator, has been studied in the detuning condition. The performance of the controller is good, even when the rotor time constant is increased from nominal rate to twice the nominal value, as well as torque variations. In this method, estimation is done quickly and accurately, and its design is simple. Simulation results for a 3-hp induction motor driven by a current-regulated pulse width modulation CRPWM inverter with an indirect vector controller are presented to validate the effectiveness of the proposed technique for the purpose of improving the performance and robustness of the drive.

This paper proposes a new control technique for Unified Power Quality Conditioner (UPQC) control system, which can generate voltage and current reference components quickly and without sensitivity to the power frequency variation. Therefore, the stability of the compensation procedure will be improved greatly. The proposed technique uses wavelet transform decomposition and Multi-Resolution Analysis to extract the fundamental component of distorted waveform and The Least Square error method for estimating frequency, amplitude and phase angle of the fundamental component. In this case, Least Square method is used for estimating the amplitude and phase angle of a sine waveform, so the proposed control technique can extract compensating components quickly and accurately. Analyzing the proposed technique for series and shunt active power filter control, as well as simulation results is presented. Results confirm that the proposed method can extract voltage and current references not only more accurately and faster than other well-known control techniques, but also without sensitivity to the frequency variation.

This paper analyzes the harmonic performance of thyristor controlled series capacitors (TCSCs) in power systems and proposes an effective method for their control and limitation in the compensated line. This is performed by proper selection of TCSC elements (capacitance and inductance) and by introducing a new method for adjusting its firing angle such that high line loadability as well as low harmonics generation is achieved. Finally, a TCSC is designed, modeled, simulated and analyzed. The main contribution is the consideration of power quality phenomena, as well as loadability in the TCSC control scheme.

This paper first proposes a competitive market structure for reactive power procurement and then develops a methodology for incorporating voltage stability problems into the model. The owners of electric transactions should participate in this competitive framework and submit their own firmness bids in ($/MW) to the Independent System/Market Operator (ISOIMO). ISO clears the market for reactive energy regarding the value of each transaction and utilization cost of reactive power on one hand, and the impact of transaction amount on the voltage security of the power system on the other hand. Here, the voltage stability margin is incorporated into the power flow equations so that the security of the power system is provided when a sudden change in load occurs. Applying the Karush- Kuhn-Tuker theorem to the proposed OPF-based reactive power market model gives the reactive power to be provided at each generation node and amount of each bilateral transaction allowed for physical operation. To illustrate an interesting feature of the proposed methodology, several case studies are carried out over the IEEE 14-bus test system using the well-known GAMS software (MINOS solver). The results show that the proposed structure can provide an incentive for both generators and consumers to support their own electricity contracts by supplying enough reactive power at each generator or load bus.

A time-varying multipath channel model for wireless systems as an extended form of Gaussian Wide Sense Stationary Uncorrelated Scattering (GWSSUS) model and a modified adaptive Constant Modulus Algorithm (CMA) for use in a CDMA system environment are presented. The large angular spread of the signal sources is considered. The post-correlation model (PCM) of data structure is used in CMA, too. The modified adaptive CMA algorithm has faster convergence and causes better radiation patterns in different array geometries to track signal sources. Comparing the signal to noise ratio at the output of the algorithm for uniform linear and circular arrays with theoretical results proves the efficiency of the presented algorithm. BER performance of the algorithm for different element numbers of uniform linear and circular array antennas with DBPSK modulation is also studied.

In this paper, a new sphere decoding algorithm is introduced which is a modification of the Viterbo-Boutros (VB) algorithm. In the proposed algorithm, the problem of the initial selection of the search sphere radius in the VB algorithm has been removed, and furthermore, the speed of the algorithm is increased. To examine the performance of the proposed algorithm, we employ it in detection of signals in code division multiple access (CDMA) and multiple-input multiple-output (MIMO) systems. Computer simulations, by using the proposed algorithm, show a significant performance improvement with respect to other suboptimal detection methods.

One of the main problems in high voltage networks is over voltages due to lightning. These over voltages, which are not possible to prevent, create problems where the insulating level of the equipment is not enough. Selecting a high insulating level will increase the costs and volume of the equipment. For the sake of decreasing insulating levels and their costs, it is necessary to control over voltages and lead them to earth by equipment like arresters. In this paper, over voltages, mostly due to lightning and its dangers to power networks, have been studied for: 1- The effect of arrester earthing resistance, 2- Tower footing resistance, 3- Capacitive voltage transformer and 4- Tower structure. An EMPT program has been used for simulation of a line and a substation of 230kv/123kv (Ahwaz-Omidieh) as a case study.