1982 gaziantep doğumluyum. 2003 D.E.Ü. Bilgisayar ve Öğretim Teknolojileri Öğretmenliği mezunuyum. Şuanda Zirve Üniversitesi Medya ve İletişim Bilimleri alanında yüksek lisans yapıyorum. MEB.'da öğretmenim.
İSTANBUL'DA FAALİYET GÖSTEREN İNŞAAT,YAPI DEKORASYON FİRMALARININ İNTERNET SİTELERİ ÜZERİNDEN SOS... more İSTANBUL'DA FAALİYET GÖSTEREN İNŞAAT,YAPI DEKORASYON FİRMALARININ İNTERNET SİTELERİ ÜZERİNDEN SOSYAL MEDYA PAZARLAMA YÖNTEMLERİ VE SOSYAL MEDYA KULLANIMLARININ GOOGLE ANALYTİCS,ALEXA VE PAGESPEED ÜZERİNDEN DEĞERLENDİRİLMESİ
... IB Misirlioglu * , HN Cologlu, M. Yildiz Faculty of Engineering and Natural Sciences, Sabanci... more ... IB Misirlioglu * , HN Cologlu, M. Yildiz Faculty of Engineering and Natural Sciences, Sabanci University, Tuzla/Orhanli, 34956 Istanbul, Turkey Abstract ... What renders defects in ferroelectric films interesting and worth studying is that the strain and ...
This paper presents a Smoothed Particle Hydrodynamics (SPH) solution to a Rayleigh-Taylor Instabi... more This paper presents a Smoothed Particle Hydrodynamics (SPH) solution to a Rayleigh-Taylor Instability (RTI) problem in an incompressible viscous two-phase immiscible fluid with an interfacial tension. The evolution of the fluid-fluid interface is numerically investigated ...
Glass fiber reinforced composite (GFRC) are widely used in all load bearing industrial applicatio... more Glass fiber reinforced composite (GFRC) are widely used in all load bearing industrial applications. It is therefore critical to understand the fatigue characteristic of GFRC to improve the material characteristics of these composites and to prevent any untoward accidents. In this paper we describe the preliminary results of fatigue test on GFRC fabricated using an in-house laboratory scale resin transfer molding system. The fatigue tests are done for different load conditions–tension compression and reverse bending. ...
A comparative study of the numerical treatments that are commonly used in Smoothed Particle Hydro... more A comparative study of the numerical treatments that are commonly used in Smoothed Particle Hydrodynamics (SPH) together with relatively a new one, namely Artificial Particle Displacement algorithm is presented. As a benchmark study, two-dimensional dam-break problem is investigated by means of weakly compressible SPH approximation using Eu- ler’s equation of motion with artificial viscosity. After adopting standard SPH discretization schemes and equations without any numerical remedies, three different treatments are sequentially tested on the dam-break problem. In weakly compressible SPH approximation, the precise calculation of the densities of the particles is vital for the overall accuracy of the solution. In order to have an improved density field, a density correction algorithm is incorporated into the numerical algorithm as a basic numerical treatment. Subsequently, XSPH velocity variant algorithm [1] and artificial particle displacement (APD) algo- rithm [2] are implemented con...
This study deals with a weakly conducting dielectric particle suspended in a quiescent background... more This study deals with a weakly conducting dielectric particle suspended in a quiescent background dielectric fluid of higher conductivity. When subject to a sufficiently strong dc electric field, the particle will undergo spontaneous rotation along an axis perpendicular to the electric field. This phenomenon was first discovered by Quincke [1], hence named Quincke rotation. Defining the ratio of í µí¼ = í µí¼/í µí¼ as the relaxation time of the surface charge and denoting fluid and solid phases with subscripts í µí± and í µí± , the fluid-particle system is unstable if í µí¼ í µí± > í µí¼ í µí± [2, 3]. The particle will maintaion its rotation when the electric field is strong enough to overcome viscous stresses. Quincke rotation is of particular significance in Electrorheological fluids used in microfluidic devices. In addition to the pressure and viscous stress couplings, Quincke rotation includes an additional electrical stress coupling between the fluid and solid phases ...
This work aims to model long-term simulations of sway-sloshing motion in a partially filled recta... more This work aims to model long-term simulations of sway-sloshing motion in a partially filled rectangular tank with different water depths and enforced motion frequencies. The lateral motion frequency of the tank is chosen so as to coincide with the lowest theoretical natural frequency for the corresponding beam of the tank and initial depth of water reserve. A truly meshless method, Smoothed Particle Hydrodynamics (SPH) is used to discretize and solve the governing equations. It is shown that numerical results of the proposed SPH scheme are in good agreement with experimental and numerical findings of the literature.
A two-dimensional incompressible smoothed particle hydrodynamics scheme is presented for simulati... more A two-dimensional incompressible smoothed particle hydrodynamics scheme is presented for simulation of rigid bodies moving through Newtonian fluids. The scheme relies on combined usage of the rigidity constraints and the viscous penalty method to simulate rigid body motion. Different viscosity ratios and interpolation schemes are tested by simulating a rigid disc descending in quiescent medium. A viscosity ratio of 100 coupled with weighted harmonic averaging scheme has been found to provide satisfactory results. The performance of the resulting scheme is systematically tested for cases with linear motion, rotational motion and their combination. The test cases include sedimentation of a single and a pair of circular discs, sedimentation of an elliptic disc and migration and rotation of a circular disc in linear shear flow. Comparison with previous results at various Reynolds numbers indicates that the proposed method captures the motion of rigid bodies driven by flow or external bo...
Incompressible smoothed particle hydrodynamics method has been used to simulate the descent of a ... more Incompressible smoothed particle hydrodynamics method has been used to simulate the descent of a solid disk in quiescent medium under gravitational acceleration. Using a single domain approach, we have studied the effects of viscosity ratio and in- terpolation scheme. Comparison with available data in the literature shows quantitative agreement.
This work aims to model flow around rigid cylinder beneath to a free surface by using a particle b... more This work aims to model flow around rigid cylinder beneath to a free surface by using a particle based Lagrangian method, namely, Smoothed Particle Hydrodynamics (SPH) which has clear advantages on modeling nonlinear violent free surface problems. This problem which is also regarded as 2-d wave making problem in marine hydrodynamics literature is carried out for three different positions of cylinder centre with two different Froude numbers. The fluid motion is governed by continuity and Eulers equations while Weakly Compressible SPH (WCSPH) approximation together with artificial viscosity term is employed for the numerical discretization of the problem domain. Hybrid Velocity- updated XSPH and Articial Particle Displacement (VXSPH+APD) correction algorithm [1] and standard density correction treatment is also added into the numerical scheme. The Reynolds number is chosen as close to 200 for all cases where three dimensionality first starts to be effective in the flow domain [2]. As the flow ...
Incompressible smoothed particle hydrodynamics method has been used to simulate the sedimentation... more Incompressible smoothed particle hydrodynamics method has been used to simulate the sedimentation of a two-dimensional rigid elliptic disc in quiescent medium in presence of an external electric field. The motion of the elliptic disc in the absence of the electric field is compared to literature data and good agreement is observed. The results show that the trajectory of the elliptic disc in presence of the electric field is strongly affected by the electrical properties of fluid and solid.
Science and Engineering of Composite Materials, 2015
ABSTRACT Fiber Bragg grating (FBG) sensors provide excellent capability for the structural health... more ABSTRACT Fiber Bragg grating (FBG) sensors provide excellent capability for the structural health monitoring (SHM) of load-bearing structures by allowing for local internal strain measurements within structures. However, the integration of these sensors to composite materials is associated with several challenges that have to be addressed to have the correct strain measurement and in turn to perform reliable SHM. One of the most important issues is the presence of uneven strain fields around FBGs, which significantly affect the response of the sensors and hence the reliability of the acquired data. The uniformity of the strain fields around sensors is important for dependable data acquisition; however, to generate such a condition, tow width-to-FBG length relationship, optical fiber configuration with respect to reinforcement fiber orientation, and crack density resulting from fatigue loading are very important factors that have to be considered. In this paper, these issues are addressed by investigating the signal properties of FBG sensors with 1 and 10 mm lengths embedded within the composite specimens during the manufacturing process. After fatigue testing of the specimens, it is shown that 1-mm-long FBGs embedded in-line with adjacent reinforcement fibers with tow widths of ∼2 mm provide much more reliable signals than 10-mm-long FBGs embedded perpendicular to adjacent tows.
ABSTRACT In this work, a two dimensional sway-sloshing for a partially filled rectangular tank is... more ABSTRACT In this work, a two dimensional sway-sloshing for a partially filled rectangular tank is modeled by solving Euler's equation of motion utilizing Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. A special treatment is introduced for the free surface particles which is an hybrid combination of Monaghan's [1] XSPH velocity variant algorithm with updated velocities (VXSPH) and artificial particle displacement (APD) algorithm [2]. The hybrid treatment presented here provides an artificial surface tension force for free surface particles thereby impeding the escape of individual particles from the free surface and keeping these particle being attached to the free surface. The time histories of free surface elevations on the left side wall of the rectangular tank are compared with experimental and numerical results available in the literature. It is shown that the VXSPH+APD treatment significantly improves the accuracy of the numerical simulations for violent flows with a free surface and lead to the results which are in very good agreement with experimental and numerical findings of the literature.
Journal of Reinforced Plastics and Composites, 2015
ABSTRACT Multi-walled triaxial hollow fibers with two different outer wall materials are fabricat... more ABSTRACT Multi-walled triaxial hollow fibers with two different outer wall materials are fabricated by core-sheath electrospinning process and integrated into epoxy matrix with or without primary glass fiber reinforcement to produce composites with enhanced mechanical properties. The morphologies of multi-walled hollow fibers are tailored by controlling the materials and processing parameters such as polymer and solvent types. The triaxial hollow fiber fabrication is achieved through using a nozzle containing concentric tubes, which allows for the transport of different fluids to the tip of the nozzle under the applied high voltage. In comparison to uniaxial electrospun fibers, the hollowness of electrospun fibers enables one to manufacture new reinforcing agents that can improve the specific strength of composites. It is shown that the mechanical properties of epoxy matrix composite incorporated with electrospun fibers as primary fiber reinforcement can be significantly tailored by properly selecting the wall materials, diameters, and the amount of electrospun fibers. We have also presented that triaxial electrospun hollow fibers as co-reinforcement in the glass fiber-laminated epoxy matrix composites enhance the flexural modulus by 6.5%, flexural strength by 14%, the onset of first layer of glass fabric failure strain by 12.5%, and final failure strain by 20%.
A novel method is presented for formation control of a group of autonomous mobile robots using pa... more A novel method is presented for formation control of a group of autonomous mobile robots using parametric and implicit descriptions of the desired formation. Shape formation is controlled by using potential fields generated from Implicit Polynomial (IP) representations and the control for keeping the desired shape is designed using Elliptical Fourier Descriptors (EFD). Coordination of the robots is modeled by linear springs between each robot and its nearest two neighbors. This approach offers more flexibility in the formation shape and scales well to different swarm sizes and to heterogeneous systems. The method is simulated on robot groups with different sizes to form various formation shapes.
ABSTRACT We study the effect of surface polarization on the distribution of free carriers in a wi... more ABSTRACT We study the effect of surface polarization on the distribution of free carriers in a wide bandgap semiconductor ferroelectric (FE) film using a thermodynamic approach. We show that free carriers, namely, holes and electrons from ionizable impurities or atomic vacancies can accumulate near the film-electrode interface, if FE polarization profile has a very steep change near the surface that is specified by the extrapolation length. Such an outcome is just the opposite of what happens in a Schottky junction in a partially or fully depleted film. This is also an entirely different effect than what has been often studied in similar structures, where the work function and screening length of the electrode metal determines the electronic character of the interface. Even for low-to-moderate densities of ionizable defects with states within the bandgap close to the band edges, high densities of carriers can localize close to the electrodes in a single domain state FE film when above a critical thickness. For very low densities of such ionizable defects, short extrapolation lengths cause electrical domain formation with minimal carrier accumulation because of the already weak depolarizing fields. This is also true for films below a critical thickness with low-to-moderate densities of ionizable impurities, i.e., electrical domains get stabilized regardless of defect density. The implications of our findings for polarization controlled Schottky to Ohmic-like transition of an interface and experimental results are discussed. It is also found that interfaces of an n-type FE heterostructure can behave like a p-type depending on the barrier heights and impurity density. We conclude that, for low-to-moderate ionizable impurity densities, it is the rate of change of polarization at the interface with position rather than solely its presence that leads to carrier accumulation and that both interfaces can become Ohmic-like with opposite signs of carriers.
... P is obtained by solving the equations of state derived from the LGD free energy for an epita... more ... P is obtained by solving the equations of state derived from the LGD free energy for an epitaxial monodomain (0 0 1) ferroelectric film on a (0 0 1) cubic substrate coupled with the Maxwell equation for dielectric displacement employing a finite difference discretization. ...
International Communications in Heat and Mass Transfer, 2015
ABSTRACT This study presents an analytical solution, for fully developed non-Newtonian fluid flow... more ABSTRACT This study presents an analytical solution, for fully developed non-Newtonian fluid flows in circular channels under isoflux thermal boundary conditions based on perturbation techniques. Since the physical properties are generally a function of temperature and may not be assumed constant under certain circumstances, the change in viscosity and thermal conductivity with temperature was taken into account. Viscous dissipation term was also included in the performed analysis. In this study, first closed form expressions for velocity, temperature distributions, and Nusselt numbers corresponding to constant thermophysical properties were given in terms of governing parameters. Then, numerical calculation was performed to obtain the values of Nusselt number and global entropy generation for variable thermophysical properties. The results revealed that neglecting the property variation significantly affects heat transfer characteristics and entropy generation, in which the deviation from the constant physical property assumption may reach up to about 32.6%.
İSTANBUL'DA FAALİYET GÖSTEREN İNŞAAT,YAPI DEKORASYON FİRMALARININ İNTERNET SİTELERİ ÜZERİNDEN SOS... more İSTANBUL'DA FAALİYET GÖSTEREN İNŞAAT,YAPI DEKORASYON FİRMALARININ İNTERNET SİTELERİ ÜZERİNDEN SOSYAL MEDYA PAZARLAMA YÖNTEMLERİ VE SOSYAL MEDYA KULLANIMLARININ GOOGLE ANALYTİCS,ALEXA VE PAGESPEED ÜZERİNDEN DEĞERLENDİRİLMESİ
... IB Misirlioglu * , HN Cologlu, M. Yildiz Faculty of Engineering and Natural Sciences, Sabanci... more ... IB Misirlioglu * , HN Cologlu, M. Yildiz Faculty of Engineering and Natural Sciences, Sabanci University, Tuzla/Orhanli, 34956 Istanbul, Turkey Abstract ... What renders defects in ferroelectric films interesting and worth studying is that the strain and ...
This paper presents a Smoothed Particle Hydrodynamics (SPH) solution to a Rayleigh-Taylor Instabi... more This paper presents a Smoothed Particle Hydrodynamics (SPH) solution to a Rayleigh-Taylor Instability (RTI) problem in an incompressible viscous two-phase immiscible fluid with an interfacial tension. The evolution of the fluid-fluid interface is numerically investigated ...
Glass fiber reinforced composite (GFRC) are widely used in all load bearing industrial applicatio... more Glass fiber reinforced composite (GFRC) are widely used in all load bearing industrial applications. It is therefore critical to understand the fatigue characteristic of GFRC to improve the material characteristics of these composites and to prevent any untoward accidents. In this paper we describe the preliminary results of fatigue test on GFRC fabricated using an in-house laboratory scale resin transfer molding system. The fatigue tests are done for different load conditions–tension compression and reverse bending. ...
A comparative study of the numerical treatments that are commonly used in Smoothed Particle Hydro... more A comparative study of the numerical treatments that are commonly used in Smoothed Particle Hydrodynamics (SPH) together with relatively a new one, namely Artificial Particle Displacement algorithm is presented. As a benchmark study, two-dimensional dam-break problem is investigated by means of weakly compressible SPH approximation using Eu- ler’s equation of motion with artificial viscosity. After adopting standard SPH discretization schemes and equations without any numerical remedies, three different treatments are sequentially tested on the dam-break problem. In weakly compressible SPH approximation, the precise calculation of the densities of the particles is vital for the overall accuracy of the solution. In order to have an improved density field, a density correction algorithm is incorporated into the numerical algorithm as a basic numerical treatment. Subsequently, XSPH velocity variant algorithm [1] and artificial particle displacement (APD) algo- rithm [2] are implemented con...
This study deals with a weakly conducting dielectric particle suspended in a quiescent background... more This study deals with a weakly conducting dielectric particle suspended in a quiescent background dielectric fluid of higher conductivity. When subject to a sufficiently strong dc electric field, the particle will undergo spontaneous rotation along an axis perpendicular to the electric field. This phenomenon was first discovered by Quincke [1], hence named Quincke rotation. Defining the ratio of í µí¼ = í µí¼/í µí¼ as the relaxation time of the surface charge and denoting fluid and solid phases with subscripts í µí± and í µí± , the fluid-particle system is unstable if í µí¼ í µí± > í µí¼ í µí± [2, 3]. The particle will maintaion its rotation when the electric field is strong enough to overcome viscous stresses. Quincke rotation is of particular significance in Electrorheological fluids used in microfluidic devices. In addition to the pressure and viscous stress couplings, Quincke rotation includes an additional electrical stress coupling between the fluid and solid phases ...
This work aims to model long-term simulations of sway-sloshing motion in a partially filled recta... more This work aims to model long-term simulations of sway-sloshing motion in a partially filled rectangular tank with different water depths and enforced motion frequencies. The lateral motion frequency of the tank is chosen so as to coincide with the lowest theoretical natural frequency for the corresponding beam of the tank and initial depth of water reserve. A truly meshless method, Smoothed Particle Hydrodynamics (SPH) is used to discretize and solve the governing equations. It is shown that numerical results of the proposed SPH scheme are in good agreement with experimental and numerical findings of the literature.
A two-dimensional incompressible smoothed particle hydrodynamics scheme is presented for simulati... more A two-dimensional incompressible smoothed particle hydrodynamics scheme is presented for simulation of rigid bodies moving through Newtonian fluids. The scheme relies on combined usage of the rigidity constraints and the viscous penalty method to simulate rigid body motion. Different viscosity ratios and interpolation schemes are tested by simulating a rigid disc descending in quiescent medium. A viscosity ratio of 100 coupled with weighted harmonic averaging scheme has been found to provide satisfactory results. The performance of the resulting scheme is systematically tested for cases with linear motion, rotational motion and their combination. The test cases include sedimentation of a single and a pair of circular discs, sedimentation of an elliptic disc and migration and rotation of a circular disc in linear shear flow. Comparison with previous results at various Reynolds numbers indicates that the proposed method captures the motion of rigid bodies driven by flow or external bo...
Incompressible smoothed particle hydrodynamics method has been used to simulate the descent of a ... more Incompressible smoothed particle hydrodynamics method has been used to simulate the descent of a solid disk in quiescent medium under gravitational acceleration. Using a single domain approach, we have studied the effects of viscosity ratio and in- terpolation scheme. Comparison with available data in the literature shows quantitative agreement.
This work aims to model flow around rigid cylinder beneath to a free surface by using a particle b... more This work aims to model flow around rigid cylinder beneath to a free surface by using a particle based Lagrangian method, namely, Smoothed Particle Hydrodynamics (SPH) which has clear advantages on modeling nonlinear violent free surface problems. This problem which is also regarded as 2-d wave making problem in marine hydrodynamics literature is carried out for three different positions of cylinder centre with two different Froude numbers. The fluid motion is governed by continuity and Eulers equations while Weakly Compressible SPH (WCSPH) approximation together with artificial viscosity term is employed for the numerical discretization of the problem domain. Hybrid Velocity- updated XSPH and Articial Particle Displacement (VXSPH+APD) correction algorithm [1] and standard density correction treatment is also added into the numerical scheme. The Reynolds number is chosen as close to 200 for all cases where three dimensionality first starts to be effective in the flow domain [2]. As the flow ...
Incompressible smoothed particle hydrodynamics method has been used to simulate the sedimentation... more Incompressible smoothed particle hydrodynamics method has been used to simulate the sedimentation of a two-dimensional rigid elliptic disc in quiescent medium in presence of an external electric field. The motion of the elliptic disc in the absence of the electric field is compared to literature data and good agreement is observed. The results show that the trajectory of the elliptic disc in presence of the electric field is strongly affected by the electrical properties of fluid and solid.
Science and Engineering of Composite Materials, 2015
ABSTRACT Fiber Bragg grating (FBG) sensors provide excellent capability for the structural health... more ABSTRACT Fiber Bragg grating (FBG) sensors provide excellent capability for the structural health monitoring (SHM) of load-bearing structures by allowing for local internal strain measurements within structures. However, the integration of these sensors to composite materials is associated with several challenges that have to be addressed to have the correct strain measurement and in turn to perform reliable SHM. One of the most important issues is the presence of uneven strain fields around FBGs, which significantly affect the response of the sensors and hence the reliability of the acquired data. The uniformity of the strain fields around sensors is important for dependable data acquisition; however, to generate such a condition, tow width-to-FBG length relationship, optical fiber configuration with respect to reinforcement fiber orientation, and crack density resulting from fatigue loading are very important factors that have to be considered. In this paper, these issues are addressed by investigating the signal properties of FBG sensors with 1 and 10 mm lengths embedded within the composite specimens during the manufacturing process. After fatigue testing of the specimens, it is shown that 1-mm-long FBGs embedded in-line with adjacent reinforcement fibers with tow widths of ∼2 mm provide much more reliable signals than 10-mm-long FBGs embedded perpendicular to adjacent tows.
ABSTRACT In this work, a two dimensional sway-sloshing for a partially filled rectangular tank is... more ABSTRACT In this work, a two dimensional sway-sloshing for a partially filled rectangular tank is modeled by solving Euler's equation of motion utilizing Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. A special treatment is introduced for the free surface particles which is an hybrid combination of Monaghan's [1] XSPH velocity variant algorithm with updated velocities (VXSPH) and artificial particle displacement (APD) algorithm [2]. The hybrid treatment presented here provides an artificial surface tension force for free surface particles thereby impeding the escape of individual particles from the free surface and keeping these particle being attached to the free surface. The time histories of free surface elevations on the left side wall of the rectangular tank are compared with experimental and numerical results available in the literature. It is shown that the VXSPH+APD treatment significantly improves the accuracy of the numerical simulations for violent flows with a free surface and lead to the results which are in very good agreement with experimental and numerical findings of the literature.
Journal of Reinforced Plastics and Composites, 2015
ABSTRACT Multi-walled triaxial hollow fibers with two different outer wall materials are fabricat... more ABSTRACT Multi-walled triaxial hollow fibers with two different outer wall materials are fabricated by core-sheath electrospinning process and integrated into epoxy matrix with or without primary glass fiber reinforcement to produce composites with enhanced mechanical properties. The morphologies of multi-walled hollow fibers are tailored by controlling the materials and processing parameters such as polymer and solvent types. The triaxial hollow fiber fabrication is achieved through using a nozzle containing concentric tubes, which allows for the transport of different fluids to the tip of the nozzle under the applied high voltage. In comparison to uniaxial electrospun fibers, the hollowness of electrospun fibers enables one to manufacture new reinforcing agents that can improve the specific strength of composites. It is shown that the mechanical properties of epoxy matrix composite incorporated with electrospun fibers as primary fiber reinforcement can be significantly tailored by properly selecting the wall materials, diameters, and the amount of electrospun fibers. We have also presented that triaxial electrospun hollow fibers as co-reinforcement in the glass fiber-laminated epoxy matrix composites enhance the flexural modulus by 6.5%, flexural strength by 14%, the onset of first layer of glass fabric failure strain by 12.5%, and final failure strain by 20%.
A novel method is presented for formation control of a group of autonomous mobile robots using pa... more A novel method is presented for formation control of a group of autonomous mobile robots using parametric and implicit descriptions of the desired formation. Shape formation is controlled by using potential fields generated from Implicit Polynomial (IP) representations and the control for keeping the desired shape is designed using Elliptical Fourier Descriptors (EFD). Coordination of the robots is modeled by linear springs between each robot and its nearest two neighbors. This approach offers more flexibility in the formation shape and scales well to different swarm sizes and to heterogeneous systems. The method is simulated on robot groups with different sizes to form various formation shapes.
ABSTRACT We study the effect of surface polarization on the distribution of free carriers in a wi... more ABSTRACT We study the effect of surface polarization on the distribution of free carriers in a wide bandgap semiconductor ferroelectric (FE) film using a thermodynamic approach. We show that free carriers, namely, holes and electrons from ionizable impurities or atomic vacancies can accumulate near the film-electrode interface, if FE polarization profile has a very steep change near the surface that is specified by the extrapolation length. Such an outcome is just the opposite of what happens in a Schottky junction in a partially or fully depleted film. This is also an entirely different effect than what has been often studied in similar structures, where the work function and screening length of the electrode metal determines the electronic character of the interface. Even for low-to-moderate densities of ionizable defects with states within the bandgap close to the band edges, high densities of carriers can localize close to the electrodes in a single domain state FE film when above a critical thickness. For very low densities of such ionizable defects, short extrapolation lengths cause electrical domain formation with minimal carrier accumulation because of the already weak depolarizing fields. This is also true for films below a critical thickness with low-to-moderate densities of ionizable impurities, i.e., electrical domains get stabilized regardless of defect density. The implications of our findings for polarization controlled Schottky to Ohmic-like transition of an interface and experimental results are discussed. It is also found that interfaces of an n-type FE heterostructure can behave like a p-type depending on the barrier heights and impurity density. We conclude that, for low-to-moderate ionizable impurity densities, it is the rate of change of polarization at the interface with position rather than solely its presence that leads to carrier accumulation and that both interfaces can become Ohmic-like with opposite signs of carriers.
... P is obtained by solving the equations of state derived from the LGD free energy for an epita... more ... P is obtained by solving the equations of state derived from the LGD free energy for an epitaxial monodomain (0 0 1) ferroelectric film on a (0 0 1) cubic substrate coupled with the Maxwell equation for dielectric displacement employing a finite difference discretization. ...
International Communications in Heat and Mass Transfer, 2015
ABSTRACT This study presents an analytical solution, for fully developed non-Newtonian fluid flow... more ABSTRACT This study presents an analytical solution, for fully developed non-Newtonian fluid flows in circular channels under isoflux thermal boundary conditions based on perturbation techniques. Since the physical properties are generally a function of temperature and may not be assumed constant under certain circumstances, the change in viscosity and thermal conductivity with temperature was taken into account. Viscous dissipation term was also included in the performed analysis. In this study, first closed form expressions for velocity, temperature distributions, and Nusselt numbers corresponding to constant thermophysical properties were given in terms of governing parameters. Then, numerical calculation was performed to obtain the values of Nusselt number and global entropy generation for variable thermophysical properties. The results revealed that neglecting the property variation significantly affects heat transfer characteristics and entropy generation, in which the deviation from the constant physical property assumption may reach up to about 32.6%.
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Papers by Mehmet Uğur YILDIZ