- PublicationOpen AccessNovel OFDM System Using Orthogonal Pilot Symbols with Subcarrier Index Modulation(Bajece (İstanbul Teknik Üniversitesi), 2019) ACAR, YUSUF; Çolak, S. AldırmazIn this work, two new transmission schemes are proposed to increase the spectral efficiency of orthogonal frequency division multiplexing (OFDM). In practical OFDM systems, channel estimation is usually performed by employing pilot symbols which is based on inserting known symbols in the time-frequency domain. However, pilot symbol designing is one of the bottlenecks of OFDM systems limiting the increase of spectral efficiency. We apply new pilot design structures, which are use orthogonal Walsh-Hadamard codes. To increase the spectral efficiency of OFDM systems, we assign the extra bits to the index of the each orthogonal Walsh-Hadamard codes. Simulation and theoretical results show that proposed methods have better performance than conventional OFDM with higher spectral efficiency. Moreover, no more energy is spent for additional information carried in the indices compared to classical OFDM systems. As a result, proposed methods provide both spectral efficiency and energy efficiency.
- PublicationMetadata onlyElectromagnetic Waves and Material Properties(2009) Yıldırım, Osman; Balta, TorehanThe standard impedance condition is the simplest way of simulating the material properties of a planar surface. This method is only accurate if the coating is very thin or lossy. To improve the accuracy, generalized impedance conditions can be used to simulate the material properties of a planar surface. The accurate solution of a scattering problem via planar slab depends on its thickness, the wavelength of incident wave, and material properties of the slab. Since boundary condition is local in character, accuracy decreases when the slab is illuminated at near grazing angle. Accuracy also decreases if the slab has a curved shape. To increase accuracy or provide a better simulation of the material, we have to search for alternative conditions. In this study, the Taylor series method is applied to a planar slab. This method gives reasonable solution even if slab has a curved shape. Power reflection and transmission coefficients are depicted versus different impedance and observation angles.
- PublicationMetadata onlyThe Speed Control of Ac Motor With Pid By Using Siemens S7-300 Plc(Int Scientific Conference SGEM, 14, Kilment Ohridsky BLVD, Sofia, 1797, Bulgaria, 2011) Kılıç, Ali; Tere, Mehmet Fatih; Yıldırım, OsmanS7 300 is the most widely used series in PLC Industry. Using this PLC, the control of 1024 input/output may be clone. In addition to this, using PLC system design is also possible. By peak output programming, complex factory projects and management can be fulfilled. Using PID control system which is one of the PLC controlling systems will be used to control AC motor speed. At the same time, the motor reactions will be tested by panel programming by changing PID values on computer screen. The purposes of the automatic control system, to keep the variable values in desired values for provide the system's stability.
- PublicationMetadata onlyUltrasonic and combustion characterization of glycerol-heavy fuel oil emulsions(Modtech Publishing House, Blvd Carol I, No 28A, Iasi, 00000, Romania, 2011) Toncu, Dana Cristina; Yıldırım, OsmanThe present study aims to draw a complete characterization of glycerol-heavy fuel oil emulsions by a novel non-invasive and fast investigation technique, which helps to determine emulsion stability and physico-chemical properties through acoustic measurements application. The reflection of ultrasonic wave on emulsion droplets, particles size and volume allows analysis of phase acoustic characters, which proved good correlation with Turbiscan, especially regarding stability and structural integrity. Further combustion tests revealed a decrease in pollutants emissions proportional to glycerol fraction addition. Moreover, NO wasn't detected in combustion gas. In order to overcome toxic acrolein atmospheric release, the combustion chamber was heated to 700 degrees C with diesel oil.
- PublicationMetadata onlyThe students' perceptions about their field at school of vocational sciences(Int Scientific Conference SGEM, 14, Kilment Ohridsky Blvd, Sofia, 1797, Bulgaria, 2010) Kahvecioğlu, Habibe; Yıldırım, Osman; 48626As it is well-known, students' vocational choice and students' personally types are very important regarding of the effectiveness of academic programs. This research aims at clarifying the relation between students' personality types and their choices by using students' perceptions. The research has been conducted on 352 students attending at School of Vocational Studies. According to the research findings, there are strong relationships between students' personality types and their choices. Based on The Five Factor Model, Inventory is an evaluation tool which is improved according to the Turkish culture. Validity and reliability analysis (dimensional self consistency cofactors vary between 0,71 and 0,88; test repeat cofactors vary between 0,83 and 0,91) show that inventory consists strong psychometric features. The results obtained from inventory were evaluated by using raw points and not norm points. In the short version of the Inventory only the five dimensions (openness for experience, responsibility consciousness, being extrovert, compatibleness, emotional balance) of the character are evaluated using total 25 attributes. The answers for the attitudes are classified in Likert scale 5. If the answers are totally suitable the grade given is 5, if totally not suitable the grade given is 1.