Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Citation - WoS: 12Citation - Scopus: 12Scattering of Waves by a Perfectly Conducting Wedge Residing at the Interface Between Two Isorefractive Media(Ieee-inst Electrical Electronics Engineers inc, 2016) Basdemir, Husnu DenizScattered field by a wedge that is surrounded by isorefractive media is analyzed. A series-based method is introduced and applied to the wedge problem with soft boundary condition. The fields are examined numerically. The numerical results show that the proposed method is suitable for analysis of these kinds of problems.Article MD study of energetics, melting and isomerization of aluminum microclusters(Springer, 2006) Böyükata, Mustafa; Güvenç, Ziya B.Voter and Chen version of an Embedded Atom Model has been applied to study the locally stable structures, energies, melting, isomerization and growth patterns of small aluminum clusters, Al(n), in the size range of n = 2 - 13. Using molecular dynamics and thermal quenching simulations, the global minima and the other locally stable structures have been distinguished from those stationary structures that correspond to saddle points of the potential energy surface. A large number (10000) of independent initial configurations generated at high temperatures has been used to obtain the stable isomers, and the probabilities of sampling different basins of attractions, for each size of the clusters. Their energy spectra have been determined and melting, and isomerization dynamics are investigated.Article Citation - WoS: 30Citation - Scopus: 31Estimation of Aperture Averaged Scintillations in Weak Turbulence Regime for Annular, Sinusoidal and Hyperbolic Gaussian Beams Using Random Phase Screen(Elsevier Sci Ltd, 2013) Eyyuboglu, Halil T.Using the random phase screen method, aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams are estimated. Prior to this estimation, the designed random phase screen setup is tested against the known results of the existing literature from the aspects of receiver intensity distribution, point-like scintillation index and aperture averaged scintillation of spherical and Gaussian beam waves. Having obtained satisfactory results, we then proceed to estimate aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams. Our findings indicate that at a fixed aperture radius of 5 cm, sine Gaussian beam exhibits the highest scintillation, annular Gaussian beam has on the other hand has the lowest scintillations. When examined against varying aperture sizes, the scintillation ordering of beams does not change. Furthermore, although larger aperture sizes achieve substantial scintillation reductions, the rate of reductions gradually become smaller. (C) 2013 Elsevier Ltd. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 3A Hybrid Maliuzhinets/Po Method for Diffraction Problems by Impedance Wedges(Elsevier Science Bv, 2011) Umul, Yusuf ZiyaThe solution of Maliuzhinets of the diffraction problem of waves by an impedance wedge is transformed into a physical optics integral. The resultant expression is suitable for the investigation of various diffraction problems having impedance wedges. The method is applied to the scattering of waves by an impedance spherical reflector with wedge structure at its discontinuity. The results are examined numerically. (C) 2011 Elsevier B.V. All rights reserved.Article Citation - WoS: 127Citation - Scopus: 135Average Intensity and Spreading of Cosh-Gaussian Laser Beams in the Turbulent Atmosphere(Optical Soc Amer, 2005) Eyyuboglu, HT; Baykal, YThe average intensity and spreading of cosh-Gaussian laser beams in the turbulent atmosphere are examined. Our research is based principally on formulating the average-intensity profile at the receiver plane for cosh-Gaussian excitation. The limiting cases of our formulation for the average intensity are found to reduce correctly to the existing Gaussian beam wave result in turbulence and the cosh-Gaussian beam result in free space (in the absence of turbulence). The average intensity and the broadening of the cosh-Gaussian beam wave after it propagates in the turbulent atmosphere are numerically evaluated versus source size, beam displacement, link length, structure constant, and two wavelengths of 0.85 and 1.55 mum, which are most widely used in currently employed free-space-optical links. Results indicate that in turbulence the beam is widened beyond its free-space diffraction values. At the receiver plane, analogous to the case of free space, this diffraction eventually leads to transformation of the cosh-Gaussian beam into an oscillatory average-intensity profile with a Gaussian envelope. (C) 2005 Optical Society of America.Publication Throughput maximisation of different signal shapes working on 802.16e mobile multihop network using novel cognitive methods(Springer-Verlag Berlin, 2010) Preveze, Barbaros; Şafak, AyselThis study proposes cognitive methods for managing the multimedia packet traffic of 802.16e system providing the dynamic spectrum sharing by TDM & OFDMA under heavy traffic conditions. The cognitive techniques are used in order to maximize the throughput of a system having different signal shapes such as video, voice or data packets. All real time voice and video packets transmissions have been provided with full success where the loss rate of data packets has been minimized using the cognitive methods. By these methods buffers are managed successfully for the given parameters, optimum buffer sizes have been formulized and it's shown that we brought the throughput up to its calculated theoretical limits for multi-hop mobile wimax (802.16e).Conference Object Citation - WoS: 6Citation - Scopus: 4Propagation of Cross Beams Through Atmospheric Turbulence(Spie-int Soc Optical Engineering, 2005) Yenice, YE; Eyyuboglu, HT; Baykal, YPropagation properties of cross beam in turbulent medium are studied. A cross beam is constructed by the sum of two highly asymmetric Gaussian beams placed along transverse axes. It is known that such beams, when propagating in free space, will exhibit contrasting diffraction behaviours; they expand widely in one axis, while they are almost nondiffracting in the other axis within useful link lengths. This behaviour allows detecting the two components and a sum component if desired separately with a practical multiaperture receiver. Bearing in mind that this property can be exploited for a diversity scheme, our present work focuses on the propagation of such beams in turbulent atmosphere. To this end, starting with a source field expression of the cross beam, the second order mutual coherence function is formulated at the receiver plane. Intensity plots describing the dependence on the source and propagation parameters on the receiver plane are provided. The results tend to confirm the applicability of the concept provided the design parameters are appropriately chosen. For a decisive assessment, however, turbulence-induced beam wander must also be examined.Article Citation - WoS: 11Citation - Scopus: 11Uniform Boundary Diffraction Wave Theory of Rubinowicz(Optical Soc Amer, 2010) Umul, Yusuf Z.Rubinowicz introduced a uniform asymptotic evaluation of the boundary diffraction wave at the transition region [Ann. Phys. (Leipzig) 378, 339 (1924)]. The uniform theory of Rubinowicz is generalized for the improved integrals of the boundary diffraction wave. The technique is applied to the scattering problem of plane waves by an impedance half-plane, and the diffracted waves are examined numerically. (C) 2010 Optical Society of AmericaArticle Diffraction Theory of Waves by Resistive Surfaces(2010) Umul, Yusuf Ziya; Yalçın, UğurDiffraction of scalar plane waves by resistive surfaces are investigated by defining a new boundary condition in terms of the Dirichlet and Neumann conditions. The scattering problems of waves by a resistive half-plane and the interface between resistive and perfectly magnetic conducting half-planes are examined with the developed method. The resulting fields are plotted numerically. The numerical results show that the evaluated field expressions are in harmony with the theory.Article Citation - WoS: 69Citation - Scopus: 74Equivalence of Structure Constants in Non-Kolmogorov and Kolmogorov Spectra(Optical Soc Amer, 2011) Baykal, Yahya; Gercekcioglu, HamzaWe find the equivalence of the structure constants in non-Kolmogorov and Kolmogorov spectra in a turbulent atmosphere. As the reference point, the spherical wave scintillation index in a non-Kolmogorov medium is used. Relations of the structure constants are found to be functions of the power law of the turbulence spectrum and the Fresnel zone. It will be useful to employ the equivalence of the structure constants in making performance comparisons found with non-Kolmogorov and Kolmogorov spectra. (C) 2011 Optical Society of AmericaBook Review Citation - WoS: 4Citation - Scopus: 5The Theory of the Boundary Diffraction Wave(Elsevier Academic Press inc, 2011) Umul, Yusuf ZiyaConference Object Comparison of physical optics integral and exact solutions for cylinder problem(2003) Umul, Yusuf Ziya; Yengel, Emre; Aydın, AyhanThe sound source composition of the urban sound environment varies depending on the geography and socio-cultural context. Current sound taxonomies in the literature categorize urban sound sources by their source types (e.g., human-made, natural, electromechanical) and respective semantic attributes. This study aims to add another taxonomical layer to the existing urban sound source categorization methods. The additional layer is a recently proposed sound source classification framework (CLIC). The CLIC framework identifies sound sources based on their Diegesis and Intention parametric attributes. The former parametric attribute, diegesis, was derived from film sound design. The geographical and socio-cultural context of the built environment can be considered as its narrative; hence, every event that happens within the functional context can be called diegetic, while the events that do not belong to that specific place can be called nondiegetic. The latter parametric attribute, intention, was derived from product design. One of the prominent sound source categorization methods in product sound design is to group the product emitted sounds as consequential and intentional. Combining these two parametric attributes with the existing taxonomies, the CLIC framework outputs a place-specific design guideline, clearly dictating the actions a sound designer should take. The two parametric attributes group the sound sources under four distinct areas, which dictates the degree of influence of designers on the specific sound source. The four zones are defined as the creation zone, limitation zone, isolation zone, and control zone. Each zone dictates step-by-step sound design instructions for the sound designer. This study consists of two main phases: field recordings and web-based listening tests. The sound sources present in the urban sound environment were identified in the field recordings phase. Later, in the web-based listening tests phase, the identified sound sources were evaluated based on the CLIC framework, and hence, their respective zones on the model were identified. The outcomes of the study propose clear step-by-step design guidelines and present action suggestions for environmental sound designers.Article Citation - WoS: 13Citation - Scopus: 13Per Unit Received Power Apertured Averaged Scintillation of Partially Coherent Sinusoidal and Hyperbolic Gaussian Beams(Elsevier Sci Ltd, 2015) Eyyuboglu, Halil T.We evaluate the per unit power received power aperture averaged scintillation performance of fully and partially coherent sinusoidal and hyperbolic Gaussian beams. Our analysis includes fundamental Gaussian, cosh Gaussian, cos Gaussian and annular Gaussian beams. The method is based on our earlier introduced semi-analytic approach. Scintillation performance is measured upon dividing the aperture averaged scintillation by the received power. Assessment is made both for aperture sizes that are adjusted separately for full and partially coherent beams to capture 10% and 20% of the equal source power and also for fixed aperture sizes. This way, the scintillation performance of the different beams in question is compared. From this comparison, we find that partially coherent beams have lower scintillation than the fully coherent ones, when adjustable aperture size is used. But upon switching to fixed aperture size, the reverse happens and coherent beams become more advantageous. In all cases of comparison, small source sized annular Gaussian beam and large source sized Gaussian beam seem to offer the lowest scintillation when aperture size is adjusted to capture 20% of the equal source power. (C) 2015 Elsevier Ltd. All rights reserved.Article Citation - WoS: 16Citation - Scopus: 33New Microstrip Bandpass Filter Designs Based on Stepped Impedance Hilbert Fractal Resonators(Taylor & Francis Ltd, 2014) Eyyuboglu, Halil T.; Ali, Jawad K.; Mezaal, Yaqeen S.The proposed microstrip bandpass filters in this paper have compact sizes and narrow band responses which are the requirements of modern wireless communication circuits. These filters are constructed from dual-edge coupled resonators; each resonator is based on applying step impedance resonator generator on first and second iteration of Hilbert fractal resonators on each segment of each iteration level. They have been designed for the industrial, scientific, and medical band (ISM) band applications at a centre frequency of 2.4 GHz using a substrate with a dielectric coefficient of 9.6 and thickness of 0.508 mm. The performance of bandpass filters has been analysed using a method of moments (MoM) based on software package, Microwave Office 2009, from Advanced Wave Research Inc., which is widely adopted in microwave research and industry. Simulation responses show that these filters possess good frequency response characteristics with second harmonics suppression. Moreover, these filters showed noticeable miniaturization which is an important feature for many communication applications. The simulated and measured results are in good agreement.Article Wave Diffraction by Material Half-Planes(Elsevier Gmbh, Urban & Fischer verlag, 2017) Umul, Yusuf ZiyaThe diffraction of E-polarized electromagnetic waves by resistive and conductive half planes is studied. The solution of Maliuzhinets for the scattering problem of plane waves from an impedance half-screen is taken into account. The diffracted fields from the resistive and conductive half-planes are obtained by using a relation between the scattered waves from material surfaces. The integrals ofscattering are also constructed in the complex plane. The resultant field expressions are compared with the literature numerically. (C) 2016 Elsevier GmbH. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 4Diffraction of Plane Waves by a Black Wedge(Elsevier Sci Ltd, 2010) Umul, Yusuf Z.The scattering of plane waves by a black wedge is examined. Two methods are considered for the solution of the problem. A closed-form series solution is derived by performing the technique of the separation of variables using boundary conditions of Macdonald. The second approach is the method of the modified theory of physical optics. The results are compared numerically. (C) 2009 Elsevier Ltd. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 1Interaction of Electromagnetic Waves With a Resistive Half-Plane(Springer France, 2016) Umul, Yusuf Z.The interaction process of electromagnetic waves by a resistive half-plane is investigated. The scattered geometrical optics fields are obtained by subtracting the incident field from the total geometrical optics waves. The physical optics integral of the scattered waves is derived with the aid of the scattered geometrical optics fields. The edge diffracted waves are derived from the physical optics integral by the edge point technique. A correction field is added to the diffracted fields in order to obtain a solution that satisfies the resistive boundary conditions on the surface of the half-screen. The uniform diffracted fields are expressed in terms of the Fresnel function and the resultant field representations are compared with the literature numerically.Article Scattering of Waves by an Aperture in an Impedance Screen(Elsevier Gmbh, Urban & Fischer verlag, 2012) Umul, Yusuf ZiyaThe transmission and diffraction of waves by an aperture in an impedance screen is investigated. The Senior's solution of the scattering problem of waves by an impedance half-plane is transformed into a physical optics type integral. The obtained method is applied to the transmission problem of waves by a slit in an impedance screen. The results are compared with the aperture problem in black and conducting screens numerically. (C) 2012 Elsevier GmbH. All rights reserved.Conference Object Citation - WoS: 3Citation - Scopus: 5Reactivity of the Nin(T) (N=54,55,56) Clusters With D2(V,j) Molecule: Molecular Dynamics Simulations(Elsevier Science Bv, 2004) Özçelik, S; Güvenç, ZB; Durmus, P; Jellinek, JThe reactive channel of the D(2) (v, j) + Ni(n) (T) (n = 54, 55, 56) collision system is studied via quasiclassical molecular dynamics simulations. The cluster is described using an embedded-atom potential, and the interaction between the molecule and the cluster is modeled by a LEPS (London-Eyring-Polanyi-Sato) potential energy function. Dissociative chemisorption probabilities are computed as functions of the impact parameter and the collision energy, and are used to evaluate the reaction cross-sections. Effects of the initial rovibrational states of the molecule and the temperatures of the clusters on the reactive channel are analyzed. Reaction rate constants are also computed and compared with those measured experimentally. (C) 2004 Elsevier B.V. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 1Application of the Method of Transition Boundary To the Half-Planes With Mixed Boundary Conditions(Elsevier Gmbh, 2020) Umul, Yusuf ZiyaThe scattering problems of waves by soft-hard and hard-soft half-planes are investigated by the method of transition boundary. The functional values at the transition boundaries are found to be identical to the ones for the soft and hard half-screens. It is shown that the factorization process should be applied by also taking into account the boundary conditions besides the principle of reciprocity. The exact diffracted field expressions are obtained for both of the half-planes.
