Scientia Iranica
Volume:20 Issue: 6, 2013

There are parser generators that accept ambiguous context-free grammars, where ambiguities are resolved via disambiguation rules, with the outcome of smaller parse tables and more efficient parsers. However, the compiler writers are expected to develop compact ambiguous grammars and extract ambiguity-resolving information from the syntax and semantics of the language. The aforementioned tasks require considerable expertise, not often owned by casual compiler writers, or even expert programmers who are assigned a serious compiler-writing task, while programming language designers are, usually, capable of providing a concise and compact ambiguous description of the language that may include ambiguity-resolving information.In this paper, we aim to provide a powerful notation for syntax definition, which enables the language designer to assert some shift and reduce sets associated with each production rule of the possibly ambiguous grammar. These sets of language tokens guide the parser generator to resolve the parse table conflicts that are caused by the ambiguities in the grammar or by other sources. The practicality of the proposed asserted shift reduce notation is supported by several examples from the constructs of contemporary programming languages and is tested to work properly via developing a parser generator that constructs conflict-free LALR (1) parse tables.

Object-Z is an extension of Z which provides specific constructs to facilitate specification in an object-oriented style. A number of contributions have been made so far to animate Object-Z with various object-oriented programming languages. However, none of the existing animation methods present their mapping rules formally. Also, none of these animation methods prove the correctness of their mapping rules. In our previous work, we informally presented an animation method to map Object-Z specifications into C++ code. In this paper, we propose a formal mapping from Object-Z specifications to C++ code. We also prove the correctness of the given mapping rules.

Over the past decades, Redundant Array of independent Disks (RAIDs) have been configured based on mechanical characteristics of Hard Disk Drives (HDDs). With the advent of Solid-State Drives (SSDs), such configurations such as stripe unit size can be far from the characteristics of SSDs. In this paper, we investigate the effect of stripe unit size on the endurance and the overall I/O performance of an SSD-based RAID array and compare the optimal stripe unit size with the suggested stripe unit sizes for HDD-based RAID. To this end, we first examine the number of extra page reads and writes imposed by write requests and then observe the corresponding impact on the overall throughput and the average response time of SSD-based RAID arrays. The effect of extra page writes for different stripe unit sizes and their impact on endurance has been also examined. To validate the analytical study, we have used I/O intensive traces and simulated an SSD-based RAID array using DiskSim simulator with different stripe unit sizes. The experimental results reveal that unlike HDD-based RAID arrays, a 4KB stripe unit size can significantly improve the throughput, response time, and endurance of an SSD-based RAID4 array (up to 67.6%, 52.2%, and 48.6%, respectively) as compared to 128KB stripe unit size.

This paper presents a practical solution to achieve a fault tolerant attitude control system capable of Fault Detection and Diagnosis (FDD). The novelty of our proposed strategy is in the accurate modeling of satellite dynamics by the Takagi-Sugeno method. Based on this model, an adaptive observer has been utilized to achieve fault diagnosis in reaction wheels of the Attitude Control System (ACS). For this, occurred faults in reaction wheels have been estimated using an adaptive algorithm which provides fault detection and identification abilities. Moreover in this paper, a recovery algorithm has been utilized combined with fault detection and identification algorithm to provide an advanced decision support system. In this regard, for undertaking the remedial actions, a backstepping feedback linearization control law has been considered, in which the estimated fault has been utilized. Accordingly, the boundedness of the attitude control error is guaranteed, despite actuators fault. The developed algorithms provide a significant degree of autonomy to effectively handle satellite operation in the presence of ACS faults without the ground segment intervention. Through extensive simulation results, the designed algorithms are shown to be robust and accurate. Also, designed algorithms are assessed through hardware in the loop test bed to evaluate their functions in a experimental situation.

In this paper, we present an efficient evolutionary algorithm for Multiuser Detection (MUD) problem in Direct Sequence-Code Division Multiple Access (DS-CDMA) communication systems. The optimum detector for MUD is the Maximum Likelihood (ML) detector, but its complexity is very high and involves an exhaustive search to reach the best fitness of the transmitted and received data. Thus, there has been much interest in suboptimal multiuser detectors with less complexity and reasonable performance. The proposed algorithm is a modified Genetic Algorithm (GA) which reduces the dimension of the search space and provides a suitable framework for future extension to other optimization problems, especially for high dimensional ones. This algorithm is compared to ML and two famous model-free optimization Particle Swarm Optimization (PSO) and Ant Colony Optimization (ACO) algorithms which have been used for MUD in DS-CDMA. The simulation results show that the performance of this algorithm is close to the optimal detector, it has very low complexity, and it works better in comparison to other algorithms.

Some applications of FACTS devices prove them proper and effective instruments for controlling the technical parameters of power systems. Applying a suitable objective function to optimal placement of FACTS devices plays a very important role in economic improvement of a power market. In this paper, an effective method has been presented for optimal placement of FACTS devices in order to increase the voltage stability and to decrease the losses considering the investment cost of the FACTS devices and the total fuel cost of the power system. Therefore, the Harmony Search Algorithm (HSA) is applied in this paper for simultaneous locating as well and for determining the sizes of both the series and parallel devices (SSSC, STATCOM) in a multi-objective structure. Since the optimization is multi-purpose, a fuzzy system is used in order to find the best solution. The effectiveness of the proposed method is demonstrated using the modified 30-bus IEEE test system. Comparing the results achieved by the suggested algorithm with those of the PSO and GA, the proper efficiency of the presented algorithm will be enforced.

This paper presents the application of Mixed-Integer Programming (MIP) approach for solving the Daily Hydrothermal Generation Scheduling (DHGS). In restructured power systems; Independent System Operators (ISOs) execute the Security-Constrained Unit Commitment (SCUC) program to plan a secure and economical hourly generation schedule for the daily/weekly-ahead market. The DHGS is a highly dimensional mixed-integer optimization problem, which might be very difficult to solve when applied for realistic power system, therefore we use MIP. This approach allows precise modeling of hydro and thermal systems that are represented in high detail. It includes valve point loadings, prohibited operating zones (POZs), dynamic ramp rate limits, non-linear start-up cost functions of thermal units, variable fuel cost, operating services, fuel and emission limits of thermal units and variable head Water-to-Power conversion function of hydro plants. To assess the approach, a study case based on an IEEE 118 bus system is performed. The effectiveness of the proposed model is shown on different test systems.

Unilateral vocal fold paralysis (UVFP) is a type of neurogenic laryngeal disorder, in which, vocal folds of patients do not have their normal behaviors, leading to abnormal talking voices. In this paper, a new noninvasive method for processing telephony speech signals is proposed to remotely diagnose the voice of the patients with UVFP disease. The proposed feature extraction method benefits from an adaptive decomposition method, the Matching Pursuit (MP) algorithm, to decompose involved signals to some predefined atoms. Then, the attributes of the obtained atoms assigned to the speech signal converts to a final feature vector so called MSDMP. Simulation results indicate the usefulness of the proposed feature vector with respect to a commonly used wavelet based features (EWPD). The MSDMP feature vector has improved the classification rate by 4.98% as compared to the EWPD feature vector.

Brain Computer Interface (BCI) is a system which straightly converts the acquired brain signals such as Electroencephalogram (EEG) to commands for controlling external devices. One of the most successful methods in BCI applications based on Motor Imagery is Common Spatial Pattern (CSP). In the existing CSP methods, common spatial filters are applied on whole EEG signal as one time segment for feature extraction. The fact that ERD/ERS events are not steady over time motivated us to break down EEG signal into a number of sub-segments in this study. Since the importance of EEG channels for classification varies for different time segments. Accordingly we extract a feature vector from each time window of EEG channels using the analysis of CSP. In order to classify a Motor Imagery EEG signals, we apply a LDA classifier based on OVR (One-Versus-the Rest) scheme on the extracted CSP features. The considered Motor Imagery four classes are: left hand, right hand, foot and tongue. We used dataset 2a of BCI competition IV to evaluate our method. The result of experiment shows that this method outperforms both CSP and the best competitor of the BCI competition IV.

In this paper، the problem of controlling chaotic uncertain brushless dc motor (BLDCM) and permanent magnet synchronous motor (PMSM)، exposed to external disturbances، is considered. First، a new nonsingular terminal sliding surface is introduced and its finite-time convergence to the zero equilibrium is proved. Then، it is assumed that the parameters of the BLDCM and PMSM are fully unknown and appropriate adaptive laws are derived to tackle the unknown parameters of the systems. Besides، the effects of models uncertainties and external disturbances are also taken into account. Afterwards، based on the adaptive laws and robust finite-time control idea، a robust adaptive sliding mode controller is proposed to ensure the occurrence of the sliding motion in finite time. It is mathematically proved that the introduced nonsingular terminal sliding mode technique has finite-time convergence and stability in both reaching and sliding mode phases. Numerical simulations are presented to verify the efficiency of the proposed method and to validate the theoretical results of the paper.

A large-signal analysis of sub-harmonic parametric oscillations in power amplifiers (PAs) is presented in this paper. Simplified models for current-voltage and channel charge characteristics of short-channel pseudomorphic high electron mobility transistors (pHEMTs) are adopted to investigate the effects of the device transconductance and gate-source capacitance nonlinearities on the amplifier stability. A 5-W Ku-band PA is designed to demonstrate application of the presented analysis. The MMIC PA is implemented in a 0.25-μm GaAs pHEMT process. Measurement results indicate that the PA features 37.5 dBm (5.6 W) average output power, 36% power added efficiency (PAE), and 18 dB average small signal gain.

In this paper, an on-chip NBTI sensor based on rise transition time di erence measurement of inverter is proposed. This sensor supports both AC and DC stress mode with very short measurement time of 50 nsec. The new sensor, with direct correlation between Vth degradation and its output voltage change, has a resolution of 1 mV per 0.5 mV threshold voltage shift. Di erential structure of the sensor eliminates the e ect of common-mode environmental variation such as temperature. A 65 nm CMOS technology model is used for simulation of the sensor. The average power consumption of this sensor is 0.14 W in stress mode and 4.54 W during measurement mode. The implemented layout area is 98.9 m2.