ارتقای کیفیت دستهبندی متون با استفاده از کمیته دستهبند دو سطحی
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Sa'eed Jalili,Ali Akbar Sadri
,
597
bagging,Text Classification – Rocchio,Naïve Bayesian,SVM,Text Clustering,Classification Committee,Bagging Committee
Nowadays, the automated text classification has witnessed special importance due to the increasing availability of documents in digital form and ensuing need to organize them. Although this problem is in the Information Retrieval (IR) field, the dominant approach is based on machine learning techniques. Approaches based on classifier committees have shown a better performance than the others. In this research, in addition to study text classification techniques and classification committees, two ideas in this field are proposed.
The first idea, is proposed based on Bagging committees. According to this idea, first, a training set by one of clustering techniques automatically is divided into several clusters based on class similarity (or dissimilarity). So for documents of every cluster, a classifier is trained and put in the committee as a member. In this approach the members of committee are created by the same technique. In our experiments for this idea, Naïve Bayesian, Rocchio and SVM learning techniques are used.
In the second idea, the creation of two layered committee is discussed. Based on this idea, one committee can be created that its members are itself a committee. Members of subcommittees are creating based on the first idea. This idea is based on the fact that if Naïve Bayesian committee acts better than Naïve Bayesian classifier and so, a committee out of these committees will improve the performance of classification.
Evaluation of the first idea showed that the improvement in performance based on precision and recall in Naïve Bayesian committee is exceeded the other committees (respectively 12 and 5.1 percent). Evaluation of the second idea showed that the improvement in performance in the second type of committee (based on the second idea) is more than that in the first type of committee (based on the first idea). Most improvement of performance in the second type of committee is referred to the Rocchio’s committee (based on precision and recall 3.8 and 18.8 percent, respectively).
http://jac.ut.ac.ir/article_307_31.html
http://jac.ut.ac.ir/pdf_307_2168c7e795fa7ee159bc62a36e60ef67.html
طراحی کنترلگر تراکم پیشبین تطبیقی برپایه مدیریت فعال صف در مسیریابهای شبکه TCP
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Mohammad Torkamandi,Mohammad Taghi Hamidi Beheshti
,
587
TCP,Congestion control,Active queue management,Random Early Detection,Controlled Autoregressive Integrated Moving Average,Adaptive Predictive Control
http://jac.ut.ac.ir/article_308_31.html
http://jac.ut.ac.ir/pdf_308_7b94639fd0af39be91b9260e3f925439.html
تنظیم پارامترهای ترانسفورماتور با استفاده از الگوریتم ژنتیک
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Ebrahim Rahimpour,Vahid Rashtchi,Esma'eel Mashhadi Rezapour
,,
615
Transformer,Genetic Algorithm,Parameter determination
http://jac.ut.ac.ir/article_309_31.html
http://jac.ut.ac.ir/pdf_309_182884ad393965b2763f72e2d04414fd.html
اندازهگیری دقیق ولتاژ الکتریکی در مبدل ولتاژ نوری با استفاده از شبکههای عصبی
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Hassan Monsef,Taher Ghomian
,
643
Integrated Optic Pockels Cell,Bulk Sensors,Optical Voltage Transducer,Electric Field,Neural Network
This paper introduces Artificial Neural Network (ANN) method for measuring voltage in the Optical Voltage Transducer (OVT) using one or more electric field sensors. In order to obtain an accurate voltage measurement with minimum number of sensors, first the locations of sensors are specified by quadrature method. Then the electric field intensity at these locations is provided to ANN for the calculation of applied voltages. Less number of sensors with no displacement required to obtain high accuracy is the most important advantage of this method. The numerical simulations demonstrate the effectiveness of this technique.
http://jac.ut.ac.ir/article_310_31.html
http://jac.ut.ac.ir/pdf_310_77603fd858dec86e04607bb45dfbef7a.html
روشی مرکب در کنترل ادوات FACTSجهت بهبود اولین نوسان حالت گذرا
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Seyyed Mohammad Azimi,Sa'eed Afsharnia
,
631
Continuous and Discontinuous Control,Lyapunov,STATCOM,SSSC,Transient State,First Swing Stability
http://jac.ut.ac.ir/article_311_31.html
http://jac.ut.ac.ir/pdf_311_36c96788046d4e5eb353fa3179fe924c.html
تعیین حد پائین واریانس خطای تخمین برای زاویه سیگنال دریافتی با استفاده از روش CRB در آنتن های آرایه ای
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Hamid Reza Bakhshi,Azar Mahmoud Zadeh
,
577
CRB,Array Antenna,Error Estimation Variance,Direction of Arrival (DOA),Cramer,Rao Bound (CRB)
One of the important issues in many of array systems such as Radar, Sonar, Mobile, and satellite telecommunications is the estimation of DOA of narrowband received signal. CRB is very important in evaluation of parameter estimation. CRB is the lower bound estimation error variance for any unbiased estimation. In this paper, the array antenna with equal distance arrays is extended in two separated subarrays. At first we study the lower bound of estimation error variance for Direction-of-Arrival in array antennas using CRB method. Then, with extending the above method, the estimation error variance for Direction-of-Arrival in array antennas with two separated subarrays is computed. It is observed that if the size of array increases, the estimation accuracy also increases. But the cost of array and complication of the system also increase. Therefore, we suggest using array antennas with separated subarrays. Furthermore, when signal to noise ratio in the communications system is low, by using of array antennas with two separated subarrays, the Direction-of-Arrival is estimated with high accuracy.
Simulation results show that as the distance between the two subarrays and the distance between the antennas increase, the estimation error variance decreases. It should be noted that the distance between antennas should not be more than wavelength of received signal. This causes the ambiguity in estimation and grows up the sidelobes
http://jac.ut.ac.ir/article_312_31.html
http://jac.ut.ac.ir/pdf_312_e32bd2392df1f0a1c751624b7f62ff4d.html
ریز ماشینکاری PET با استفاده از لایه برداری شیمیایی در حضور
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Nima Izadi,Amir Samak,Shamsoddin Mohajerzadeh
,,
567
Vertical etching,Ultra,Violet,Micro,Patterns,Chemical Solution
In this paper, we report vertical etching of poly-ethylene-terephtalate plastic substrates by means of a chemical solvent and in the presence of ultra-violet illumination. Since the PET substrate is not dissolved in solvent without a UV source, only the desired areas with proper opening for UV exposure are removed in a vertical fashion. The etch rate varies between 1 and 8 micrometer per minute, depending on the process conditions. Various structures such as micro-gears and interdigital structures have been realized using this approach. Combining this method with electroplating, the fabrication of micro-motors, micro-valves and optical devices would be possible.
http://jac.ut.ac.ir/article_313_31.html
http://jac.ut.ac.ir/pdf_313_49e3929160ee9f4ed66fc27ca14b8c84.html
بررسی اثر تزویج متقابل بر مشخصات تشعشعی یک آرایه آنتن مسطح محدود شامل پچ های مستطیلی
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Fa'egheh Amirzadeh,Mahmoud Kamare'i,Gholamreza Dadashzadeh
,,
557
Input Impedance,Mutual Impedance,Microstrip Antenna Array,Moment Method,Mutual Coupling
In this paper a novel method for computing the radiation pattern and also the input impedance of a planar rectangular micro-strip antenna array with consideration of mutual coupling and mutual impedance is presented. Each two triangles with a common edge make an Edge element or RWG. Any such edge element is considered as an infinitesimal dipole. The electrical currents over each dipole can be calculated by solving an electric field integral equation (EFIE), using the method of moments. Using the resulting surface currents and considering the mutual coupling effect between the elements, the radiation pattern of the whole array is obtained employing a new method, which we call it “active element pattern based on RWG edge element”. Moreover, using the above mentioned model for the edge elements and also considering the mutual impedance between the elements, the input impedance of the array is now calculated.
http://jac.ut.ac.ir/article_314_31.html
http://jac.ut.ac.ir/pdf_314_e1d29d854343ce9a300633ad6dfb5c8e.html
روشی مبتنی بر تئوری گراف جهت تعیین بهینه جزیره ها در فرآیند بازیابی
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Hossein Afrakhteh,Mahmoud Reza Haghifam
,
541
Genetic Algorithm,Energy Not Supplied (ENS),Graph Theory,Island Load Restoration,Power System Restoration
In this paper, effect of the islands number variation in restoration process is investigated and a graph based method for determination of optimum islands boundaries is presented. Also, the effect of number and location of black-start units on the restoration process is evaluated. In optimization process, objective function is minimizing Energy Not Supplied (ENS) and constraints are voltage margins in buses, transmission lines capacities and generators loading limits. The ENS is evaluated based on generation capacity allocation to demand loads method. Genetic algorithm (GA) is the base of optimization and a suitable chromosome coding is developed to network modeling and applying to the algorithm. In order to assess the capabilities of proposed method, the IEEE-118 bus network has been used as test system and the results of sectionalizing the test system to 2, 3, 4, 5, 6 and 7 islands and the optimum boundaries of each island have been given in case studies section.
http://jac.ut.ac.ir/article_315_31.html
http://jac.ut.ac.ir/pdf_315_1815ef0fe1fa5abc2398b72f32104511.html
معرفی و شبیه سازی روش جدید اندازه گیری ضریب تلفات عایقی و پرمتیویته نسبی
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Hassan Abravesh
535
Dielectric Measurement in Time and / or Frequency Domain,Dissipation Factor,Relative Permittivity
For evaluating quality of electrical insulation, it is necessary to measure the property of insulators. Dielectric constant and loss tangent (tans) are two important parameters for determining the property of insulator. The measurement of above parameters is normally based on the time- domain and frequency-domain, which is costly and time consuming.
In this study a multiple-frequency binary sequence signal was applied to the specimen, which is a periodic voltage that switches rapidly between two presets values. Since the applied voltage is periodic, therefore the results are obtained by using a numerical Fourier series analysis. The difficulties associated with Fourier transform are avoided. By applying the above method, capacitance (dielectric constant) and loss tangent is measured over a wide range of frequency.
http://jac.ut.ac.ir/article_316_31.html
http://jac.ut.ac.ir/pdf_316_b6f0deb3db0ab9830b493b11128c1144.html
تحلیل و طراحی تغییر دهنده فاز N - بیتی MEMS توزیع شده در باند Ka
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Habibollah Zolfkhani,Jalil Rashed Mohassel,Farrokh Hojjat Kashani
,,
623
Phased Array,MEMS,Phase shifter,Switch,Full,Wave Analysis,Finite Element,Scattering Matrix,T,matrix,Insertion Loss,Return Loss
Modern microwave and millimeter wave phased array antennas are attractive because of their ability to steer wave beams in space without physically moving the antenna element. A typical phased array antenna may have several thousand elements fed by a phase shifter for every antenna, which can steer the resulting array beam to different directions. Their low loss, low cost and lightweight phase shifters are important for the design of phased array antennas. The ferrite phase shifters have low insertion loss and can handle significantly higher powers, but they are complex in nature and have a high fabrication cost. While semiconductor phase shifters using PIN diodes or FET’s are less expensive and smaller in size than ferrites, their application is limited because of high insertion losses. Recently, others types of phase shifters using MEMS technology have been investigated to overcome the above limitations.
This paper presents analysis and design of distributed MEMS phase shifters for Ka-band communication systems. The phase shift can be obtained by changing MEMS bridge capacitors located periodically over the transmission line. Simulation results of phase shifters with various structural parameters are analyzed to develop the optimized designs. It is observed that the distributed microelectromechanical transmission-line (DMTL) phase shifter can be accurately modeled using a combination of full-wave electromagnetic and microwave circuit analysis. The full-wave electromagnetic simulation of the unit cell is done by finite element using Ansoft High Frequency Structure Simulator (HFSS). After the full wave analysis is performed, S-parameters are extracted in the frequency range going from 26 to 40 GHz for different widths and heights of the MEMS bridge. S-parameter presentation of phase shifters is very important in computer aided design (CAD). Finally, the S-parameters are combined to obtain the overall phase shifter performance over Ka-band. This phase shifter offers the potential for building a low loss device for a variety of phased arrays and radar. The average insertion loss and return loss and the phase errors of our phase shifter are compared with the reported MEMS phase shifters at various references.
The overall performance of n-bit phase shifter is obtained, using S-parameters and microwave circuit theory. Using phase shifts versus numbers of cells, it is shown that the n-bit phase shifter can be obtained with a suitable combination of one-bit phase shifters with 11.25, 22.5, 45, 90 and 180 degrees. Insertion losses, return losses, and phase shifts ware obtained in 32-states at the frequency range 26-40 GHz. Average insertion loss –1.68 dB, return loss –11.94 dB, and phase errors of 2.33 was obtained in 33 GHz for 4-bit phase shifter. The results are in good agreement in comparison with the reported MEMS phase shifters.
http://jac.ut.ac.ir/article_317_31.html
http://jac.ut.ac.ir/pdf_317_6e9b056bd104d311c51d23a37c6c5019.html
ارزیابی قابلیت اطمینان تولید در بازار برق رقابتی کامل
University of Tehran
Journal of Algorithms and Computation
2776-2476
2476-2784
2013
05
41
5
No
2013-05-18
Hossein Harounabadi,Mahmoud Reza Haghifam,Mahmoud Fotouhi Firouzabad
,,
653
Generation Reliability,Perfect Competition Power Market,Monte Carlo Simulation
Deregulation policy has caused some changes in the concepts of power system reliability assessment. This paper deals with generation reliability evaluation in perfect competition power market using market economic concepts and its dynamic. Also, because of power markets and generators’ forced outages stochastic behavior, Monte Carlo Simulation (MCS) is used in this research. Generation reliability merely focuses on interaction between generation complex and load, and it’s supposed that transmission and distribution systems are reliable. Therefore, this paper using perfect competition market subjects and demand-offer curves interaction, deals with generation reliability evaluation. The proposed method is assessed on IEEE-Reliability Test System (IEEE-RTS), and reliability indices are evaluated with various parameters.
http://jac.ut.ac.ir/article_318_31.html
http://jac.ut.ac.ir/pdf_318_a92335d5b367048640e38b740b74b698.html