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A parallel hybrid system of HMM and GMM modeling techniques was implemented and used in a telephony speaker verification and identification system. Spectral subtraction and Weighted Projection Measure were used to render this system more robust against additional noise. Cepstral Mean Subtraction method was also applied for the compensation of convolution noise due to transmission channel degradation and differences in the frequency response of telephone handsets. For a population of 100 speakers of FARSDIGITS1 database with a SNR of 8.8 dB, a speaker identification performance of 95.51% and a speaker verification error rate of 0.37% were obtained. Several score normalization methods in utterance and frame level and weighting of model scores were also implemented, and then compared and evaluated. It was shown that these methods improve discrimination between speakers and yield a reduction of speaker verification and identification error rates.

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The aim of this article is to compare a direct hybrid system of gas turbine and solid oxide fuel cell with an indirect system from thermodynamic and exergy viewpoints. According to importance of fuel cell role in hybrid cycles and providing further proportion of produced power, discrete and complete thermodynamic, electrochemical and thermal analyses have been done. Calculation of working temperature which has an impact on system performance is one of the most significant works that is done in this article. In addition, by parametric study of this hybrid system, the influence of inlet air rate and compression ratio on efficiency, power and exergy destruction rate has been perused and eventually an optimized state for system will be offered. Results indicate that a direct hybrid system is more efficient in comparison with an indirect system. Higher efficiency, less irreversibility, higher power, and less pollution are the most important advantages of direct hybrid systems.

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In recent years, development of effective devices for seismic energy dissipation in structures has become more important to keep response of structure in elastic range. Dampers are used in structures to reduce response and effect of seismic forces. Also, using secondary mass technology can help seismic energy dissipation. Among these systems one can mention tuned mass damper and tuned liquid column damper, working base on secondary inertia in structures. In this paper, hybrid system of tuned mass & liquid column dampers in series was considered with mass ratios 0.035-0.005, 0.03-0.01 and 0.02-0.02. Time history analysis using the Northridge, Tabas and Loma Prieta earthquakes for 20 story structures were modeled in Simulink Matlab software considering shearing structure and damper modeling in every blocks separately. Effect of damper to structure is determined as forces applying on corresponding story. Performance indices using software outputs such as root mean square and Maximum of displacement and acceleration of stories were calculated. Performance of single and hybrid systems has been compared due to different earthquakes. Also effect of hybrid systems in series was studied by increasing head loss coefficient. Results show that performance of hybrid systems is dependent on earthquake characteristics that improves with increasing secondary mass ratio. For example under the Northridge earthquake, hybrid system in series tuned mass & liquid column damper with mass ratios 0.035-0.005, 0.03-0.01 and 0.02-0.02 decrease root mean square of displacement of stories 45, 27 and 2 percent respectively and also by selecting optimum frequency ratio based on responses of structure. For example maximum acceleration of hybrid system of tuned mass & liquid column damper in series with mass ratio 0.035-0.005 is optimum frequency ratio in 2.9 and also by selecting this frequency ratio decrease maximum acceleration of up and down stories in 20 story structure. By comparing effects of hybrid system Tuned Mass & Liquid Column Damper in series with different mass ratios on two structures with periods of 1.5 and 2.44 second are considering where by increasing stiffness of structure, performance of hybrid system was improved leading to decrease of acceleration responses and reduction of displacement responses. For example, J1 in 20 story structure with period 1.5 second is 0.71 whereas in other structure is 0.79 that show hybrid system has better performance in structure with period 1.5 second. Hybrid system in series damper with mass ratio 0.035-0.005 have best performance to reduce displacement stories of 20 story structure with period 1.5 second as J3=0.56 means decrease 44%. Also in other structure, hybrid system with mass ratio 0.035-0.005 has best performance to reduce displacement at top floor with J4=0.56. Also performance of hybrid system to reduce maximum displacement of stories was improved by increasing head loss coefficient in tuned liquid column damper

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In this article, stability analysis for Stochastic Piecewise Affine Systems which are a subclass of stochastic hybrid systems is investigated. Here, additive noise signals are considered that does not vanish at equilibrium points. These noises will prohibit the exponential stochastic stability discussed widely in literature. Also, the jumps between the subsystems in this class of stochastic hybrid systems are state-dependent which make stability analysis more complex. The presented theorem considering both additive noise and state-dependent jumps, gives upper bounds for the second stochastic moment or variance of Stochastic Piecewise Nonlinear Systems trajectories and guarantees that stable systems have a steady state probability density function. Then, linear case of such systems is studied where the stability criterion is obtained in terms of Linear Matrix Inequality (LMI) and an upper bound on state covariance is obtained for them. Next, to validate the proposed theorem, solving the Fokker Plank equations which describes the evolution of probability density function, is addressed. A solution for the problem of boundary conditions that arises from jumps in this class of systems is given and then with finite volume method the corresponding partial differential equations are solved for a case study to check the results of the presented theorem numerically.

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Hybrid systems are a group of dynamical system which their behavior described by the interaction of discrete and continuous dynamical system behaviors. One of the subsets of hybrid systems, is piecewise affine system. Piecewise affine system identification, consists of estimating the parameters of each subsystem and the coefficients of the state-input boundary hyperplanes. In order to clustering the state-input space and estimating the feature matrixes simultaneously, bounded error algorithm and adaline neural network are used. It should be said that in this method, there is no need to know the number of linear subsystems of the piecewise affine system. Moreover, it should be noted that the identification method is extended based on on-line data acquisition from system. In continuation, this method is used to identify a benchmark mathematical piecewise affine system. By comparing the results with the reference paper, it is proven that this method has a good performance in clustering the state-input space and estimating the feature matrixes. In the end, by using the proposed method, an active water tank which its equations are described by the form of a piecewise affine system is identified.

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Solid oxide fuel cells competence in combination with gas turbine cycle has caused the obtained synthetic system to become as a new power production system in consideration of different researchers. One of the important applications of this type of hybrid systems is to use them in UAV propulsion systems and in airliners as an APU. The main purpose of this research is design of a hybrid APU equipped to solid oxide fuel cell that would be one of the basic requirements for electric power generation in larger aircrafts in the future. Design parameters and decision-making variables in analysis of this system are the compressor pressure ratio, gas temperatures entrance to turbine and the number of selected cells. The results show that the system’s increasing pressure causes decrease in the temperature of outlet gases from the turbine and the cell’s operating temperature; and this problem severely affects the productivity and efficiency of the electrical system. At 1000 ° C for entrance gases to the turbine, electrical efficiency of system is about 49 percent. Also, the maximum electrical efficiency of the system in fuel cell is estimated to be about 55 percent. The obtained result shows that in case of controlling the generated heat in the cell and effective usage of it, the overall system efficiency will be augmentable about 84 percent. On the other hand, increasing the number of cells will cause increasing electrical efficiency and reducing the overall efficiency of the fuel cell hybrid system.

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The present study was undertaken to design and analyze three different configurations of SOFC (solid oxide fuel cell) and MGT (micro-gas turbine) hybrid system. The first presented configuration is a hybrid system with one fuel cell which considered as a basic mode. Two other configurations are considered with two fuel cells that mounted upstream of the turbine in series and parallel forms. The aim of the current study was thermodynamic analyze of designed hybrid systems and achieving the optimum fuel consumption factor for fuel cells that used in hybrid systems. Therefore, other performance parameters such as turbine inlet temperature, compressor pressure ratio and the number of cells, which play an important role in implementation of SOFC and gas-turbine, were parametrically analyzed and the obtained optimum values were used in analyzes. In this regard, the parameters associated with electrochemical processes within cells considered as a function of their chemical and thermodynamic conditions, and their modeling code combined with the modeling code of micro gas turbine cycle. The results of this study revealed that fuel utilization factor has direct impact on the SOFC/MGT hybrid system performance. Also we demonstrate that the optimal fuel utilization factor for basic mode hybrid system was 0.85, hybrid system with 2 series fuel cells were obtained 0.7 and 0.8 respectively and hybrid system with two parallel fuel cells were calculated to be 0.85. Moreover, the SOFC/MGT hybrid system with two series fuel cells account for the highest electrical efficiency and was selected as the most efficient configuration.

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In this research, the effect of using two solar fields in a solar thermal power plant was evaluated. The average price of natural gas in the last decade was 3.5 dollar/MMBTU. Due to the complexities of the solar power plant, two methods were introduced to optimize the area of the solar fields. Then, for further evaluation of the solar power plant with two distinct solar fields, the plant was examined for two natural gas prices of 3.5 and 9 dollar/MMBTU. The results of the study show that the use of two separate solar fields to produce high pressure steam turbines and low pressure over the use of a solar field reduces the cost of generating electricity. Although each solar field must produce different energy quantities, and the area of each of the fields is different, the size of the field coefficient of the field was the same for both solar fields.

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