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Öğe Applications of Genetic Algorithm to Quantum Mechanical Systems(2006) Şahin, Mehmet; Atav, Ülfet; Tomak, MehmetGenetic algorithm (GA) inspired by the biological world is a general search and optimization method. It was first proposed by Holland in 1975. GA has been applied to many scientific areas especially in engineering optimization problems. It is also used in solving of quantum mechanical problems. In this study, we have applied this method to different realistic quantum mechanical problems of both self-consistent and non-self-consistent type. The results obtained are compared with the results of other methods and it is seen that the GA can be a very powerful alternative to some other traditional techniques such as variational method. © TÜBİTAK.Öğe Bilyeli Öğütme Süresinin Garnet Benzeri Li7La3Zr2O12 Li-iyon İletkeninin Sentezine Etkisi(Selçuk Üniversitesi Fen Fakültesi, 2018) Özkendi̇r, Osman Murat; Aktaş, Sevda; Atav, Ülfet; Ateş, Şule; Çeli̇k, GültekinBu çalışmada lityum karbonat (Li2CO3), lantan oksit (La2O3) ve zirkonyum oksit (ZrO2) maddelerine mekaniksel karışım ve ardından ısıl işlem uygulanarak Li7La3Zr2O12 Li-iyon iletkeni sentezlenmiştir. Sentez sırasında uygulanan farklı öğütme sürelerinin kristal yapıdaki faz oluşumlarına, morfolojik özelliklere ve parçacık boyutlarına etkisi X-ışını kırınımı deseni (XRD) ve taramalı elektron mikroskobu (SEM) ile incelenmiştir. Elde edilen yapıya ait XRD görüntüsünün MAUD yazılımı ile yapılan ayrıntılı kristal yapı analizi, ilk öğütme süresinin Li7La3Zr2O12 kristalinin yüksek iyonik iletken faz sentezinde etkili olduğunu gösterirken son öğütme süresinin ise kristalite boyutunda etkili olduğunu göstermiştir.Öğe Binom Katsayıları Kullanarak Tek Merkezli Overlap, Potansiyel Enerji ve Kinetik Enerji İntegrallerinin Slater-Tipi Orbitaller Üzerinden Hesaplanması(Selçuk Üniversitesi Fen-Edebiyat Fakültesi, 2001) Özmen, Ayhan; Yakar, Yusuf; Sezer, Mahmut Özgür; Atav, Ülfet; Yüksel, HüseyinSlater tipi orbitaller kullanılarak tek-merkez overlap, potansiyel enerji ve kinetik enerji integralleri binom katsayıları cinsinden analitik ifadeler olarak elde edilmiştir. Bu Integraller farklı kuantum sayıları ve farklı perdeleme sabitleri için hesaplanmış, hesaplarda merkezi işlem birimi (CPU) zamanlarının faktöriyelli ifadelere göre küçük olduğu tespit edilmiştir.Öğe Computation of Two-Center Coulomb Integrals Over Slater-Type Orbitals Using Elliptical Coordinates(John Wiley & Sons Inc, 2003) Özmen, Ayhan; Karakaş, Aslı; Atav, Ülfet; Yakar, YusufA general analytic formula is obtained for the two-center Coulomb integrals over Slater-type orbitals in elliptical coordinates. Finite series expansions are used in the evaluation of the radial part of the integrals. The analytic formula is expressed in terms of a product of the well-known auxiliary functions A,(p) and B,(p) and incomplete gamma functions. Recursive relations for the computer evaluation of these functions are given as well. The recursive relations are stable and our computer results are in good agreement with the benchmark values given in the literature.Öğe Equation of State of Asymmetric Nuclear Matter: A VMC Study(De Gruyter Open Ltd, 2010) Manisa, Kaan; Atav, Ülfet; Sarıaydın, SibelA Variational Monte Carlo (VMC) method is employed to investigate the properties of symmetric and asymmetric nuclear matter. The realistic Urbana V (14) twonucleon interaction potential of Lagaris and Pandharipande was used to describe the microscopic interactions. Also, many body interactions are included as a density dependent term in the potential. Total kinetic and potential energies per particle are calculated for asymmetric nuclear matter by VMC method at various densities and isospin asymmetry parameters. The results are compared with data found in literature, and it was observed that the results obtained in this study reasonably agree with the results found in the literature. Also, the symmetry energy and incompressibility factor of the nuclear matter were obtained. The results obtained are in good agreement with those obtained by various authors with different methods and techniques.Öğe Evaluation of Two-Center One- and Two-electron Integrals Over Slater Type Orbitals(Wiley-V C H Verlag Gmbh, 2006) Yakar, Yusuf; Özmen, Ayhan; Atav, ÜlfetA formulation previously presented by the authors for coulomb integrals was generalized to other two-center integrals, except exchange integral. Within this frame, molecular integrals were expressed in terms of some new functions closely related to the well-known incomplete gamma functions and these functions recursively evaluated. Special issues arising in the case of hybrid integrals were addressed, and the results were compared with the ones found in the literature.Öğe Faz Geçişlerinin Nitel Tanımı: Kritik Üsteller(Selçuk Üniversitesi Fen-Edebiyat Fakültesi, 2003) Akgöbek, Gülenay; Yıldırım, E. Öznur; Güleç, Atilla; Akın, Erhan; Atav, ÜlfetÇok parçacıktan oluşan sistemler, parçacıklar arasındaki etkileşimler dolayısıyla parçacıkların ortaklaşa hareket etmeleri sonucunda kritik noktalarında faz geçişine uğrarlar. Bu tür kritik olaylar, çeşitli modeller yardımıyla nicel olarak incelenebilmektedir. Ancak, başlıkta da verildiği gibi bu tür olaylar, kritik üsteller aracılığıyla nitel olarak da ifade edilebilmektedir. Bu çalışmada, kritik üstellerin tanımı, aralarındaki ilişkiler ve saf sıvı sistemleri ile manyetik sistemler için deneysel veriler sunulmuştur.Öğe Fermi Sıvıları Teorisi ve Nükleer Maddenin Kararsızlık Durumları(Selçuk Üniversitesi Fen-Edebiyat Fakültesi, 2001) Güleç, Atilla; Atav, Ülfet; Oğul, RızaAtom çekirdeğinin yapısının ve fiziksel özelliklerinin araştırılması, yani nükleer maddenin değişik sıcaklık ve basınç altındaki davranışının incelenmesi, sıcaklık, basınç ve yoğunluğa bağlı olarak faz dönüşümlerinin araştırılması ve durum denkleminin elde edilmesi, nükleer fiziğin başlıca araştırma konularındandır. Nükleer maddenin fiziksel özelliklerinin incelenmesinde Landau’nun geliştirmiş olduğu Fermi sıvıları teorisi kullanılmış ve elde edilen teorik sonuçların literatürde bulunan deneysel sonuçlarla oldukça iyi uyum sağladığı görülmüştür.Öğe Ground State of Interacting Many Boson Systems: An Approach Based On Natural Orbitals(AMER INST PHYSICS, 2009) Akbaş, Hatice Zehra; Atav, ÜlfetWe have developed an alternative approach to investigate the ground state properties of many boson systems with interactions in a harmonic trap. The method is inspired, and to some extent similar to the Kohn-Sham formulation of the density functional theory. The method is applied to a model many boson system to obtain the ground state properties of the system We give a description of a many boson system within the second quantization formalism. We employ the natural orbitals to describe the ground state of the system. We represent the natural orbitals as an expansion in terms of a complete set. We obtain the expansion coefficients by minimizing the total energy. We apply the proposed method to a model system of interacting bosons. The results are compared with the results obtained from Gross-Pitaevskii equations which are widely used to describe Bose-Einstein Condensation. Also we compare our results with the Monte Carlo simulation results found in the literature The agreement of our results with the results of Gross-Pitaevskii equations establishes the feasibility and accuracy of the methodÖğe Harmonik Olarak Tuzaklanmış Bozonlarda Bose-Einstein Yoğuşması(Selçuk Üniversitesi Fen-Edebiyat Fakültesi, 2008) Öztürk, Teoman; Atav, ÜlfetBu çalışmada anizotropik bir tuzakta harmonik olarak tuzaklanmış alkali atom gazlarında gözlenen Bose-Einstein yoğuşmasına uğramış bir sistemin özellikleri incelenmiştir.Öğe İki Merkezli EFG İntegrallerinin Guseinov Açılım Yöntemi İle Hesaplanması(Selçuk Üniversitesi Fen-Edebiyat Fakültesi, 2001) Akın, Erhan; Atav, Ülfet; Özmen, Ayhan; Yüksel, HüseyinBu çalışmada iki atomlu moleküllerde, molekülün herhangi bir çekirdeğinde molekül elektronları tarafından oluşturulan elektrik alan gradyentini hesaplamada karşılaşılan iki merkezli elektrik alan gradyenti integrallerinin hesabı için Guseinov’un Slater-tipli atom orbitallerini bir merkezden başka bir merkeze taşıma yöntemi kullanılarak seri açılımlı analitik ifadeler elde edildi. Bu analitik ifadelerden integral değerlen bilgisayarla hesaplandı. Sonuçların literatürde bulunan değerlerle uyum içinde olduğu görüldü.Öğe Investigating the Droplet Formation in a Nucleonic Vapor(Royal Swedish Acad Sciences, 2003) Oğul, Rıza ; Atav, ÜlfetThe droplet formation in a supersaturated vapor which may occur during the expansion of an excited blob of nuclear matter in the metastable region at subnuclear densities is investigated. The free energy change accompanying the formation of a drop is calculated as a function of droplet radius for various saturation ratios on the basis of Fisher's model. The results are related to the experimental data.Öğe Study of the local structure and electrical properties of gallium substituted LLZO electrolyte materials(ELSEVIER SCIENCE SA, 2019) Aktaş, Sevda; Özkendir, Osman Murat; Eker, Yasin Ramazan; Ateş, Şule; Atav, Ülfet; Çelik, Gültekin; Klysubun, WantanaThe solid-state lithium batteries are more stable than the batteries with liquid electrolyte, however their performance are also worse especially due to the low ionic conduction of their electrolyte. Garnet-type Li7La3Zr2O12 is a promising solid-state electrolyte candidate for lithium batteries. In this work the influence of gallium substitution on the electrical, crystal and electronic structure properties in the Li7La3Zr2O12 material were studied. Li7-3xGaxLa3Zr2O12 solid electrolytes were synthesized by solid state reaction method and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), AC impedance spectroscopy and X-ray absorption spectroscopy (XAS) techniques. XRD and XAS analyses showed that the x = 0.05 sample is formed in the tetragonal phase with a space group of I4(1)/ acd:2 and the rest are formed in the cubic phase with a space group of I-43d due to strong coupling between outer shell electrons of the oxygen (O) and gallium (Ga) atoms. Electrochemical impedance spectroscopy (EIS) studies indicated that the tetragonal phase has the highest ionic conductivity, 3.04 x 10(-6) S cm(-1), among all other cubic phases. (C) 2019 Published by Elsevier B.V.Öğe Variational Monte Carlo Calculations of Nuclear and Neutron Matter(Royal Swedish Acad Sciences, 2000) Atav, Ülfet; Oğul, RızaUsing the Jastrow approach in choosing the variational wave functions, we have investigated symmetrical nuclear matter and neutron matter on the basis of the Variational Monte Carlo method. A function of Woods-Saxon form for two particle correlation and Urbana V-14 potential for the nucleon-nucleon interactions were used in the calculations. In order to simulate three and more particle interactions, the strongly repulsive short range part of the Urbana potential was assumed to depend linearly on the density of the matter. The total, kinetic and potential energies per particle were obtained as a function of density for nuclear and neutron matter. We observe that the results are in good agreement with those obtained by various authors with different potentials and techniques.
