Modeling dynamics and stability of 5-axis milling processes

5-axis milling is an important machining process for several industries such as aero-space, automotive and die/mold. It is mainly used in machining of sculptured surfaces where surface quality is of extreme importance. Being one of the most important prob-lems in machining, chatter vibrations must be avoided in manufacturing of these com-ponents as they result in high cutting forces, poor surface finish and unacceptable part quality. Chatter free cutting conditions for required quality with higher productivity can be determined by using stability models. Up to now, dynamic milling and stability models have been developed for 3-axis milling operations; however the stability of 5-axis proc-esses has never been modeled. In this paper, a stability model for 5-axis milling opera-tions is proposed. The model can consider the 3D dynamics of the 5-axis milling proc-ess including effects of all important process parameters including lead and tilt angles. Due to the complex geometry and mechanics of the process, the resulting analytical equations are solved numerically in order to generate the stability diagrams

Fluctuations and dissipation in a Bose-Einstein condensed photon gas

Bose-Einstein condensation, superfluidity and superconductivity are all related phenomena where particles behave as collective quantum systems. The behavior of such systems is treated using quantum statistics and their properties such as energy distribution or coherence are used to describe the system at a macroscopic level. These quantities are affected not only by the intrinsic features of the particles that constitute the quantum gas, but also by the interaction of these particles with their environment. The effect of a coupling of the quantum gas with its surroundings can be as drastic as completely changing its coherence properties or it might lead to a slight deviation from an equilibrium energy distribution. In this thesis, we investigate the effects caused by coupling a quantum gas of light with its environment. Quantum gases of light are realized in optical microcavities filled with a medium the photons couple to. If a strong coupling between the light and the medium is realized, the gas comprises mixed states of matter and light such as polaritons. Phenomena like lasing, Bose-Einstein condensation and superfluidity can be observed in such systems. In the opposite case, when the coupling of medium and photons is weak, no coherent coupling is established and the gas consists of pure photons. The latter situation can be experimentally realized in high quality optical microcavities filled with photo-excitable dye molecules. In this system it was shown that if the lifetime of the photons in the cavity are sufficiently long, they thermalize at the temperature of the dye solution. And if the density of the photons is increased beyond a critical point, a Bose-Einstein condensate of photons forms. A distinct feature of a condensate of photons in the dye-microcavity system compared to atom or polariton condensates is that the dye molecules act as a reservoir of particles, as well as energy. The photon gas exchanges particles with excited dye molecules and the coupling between the two is of statistical nature. It has been shown that Bose-Einstein condensation can coexist with unusually large particle number fluctuations in the so called grand-canonical statistical ensemble regime. In the first part of this thesis, we experimentally investigate the fluctuation-dissipation relation in a Bose-Einstein condensate of photons realized in the dye-microcavity. In equilibrium, thermally driven fluctuations are closely connected to how the system dissipates its excess energy or particles. This relation is so general that it has been observed in a variety of systems ranging from Brownian particles to quantum gases of atoms. However, its validity in Bose-Einstein condensates has not been shown. Despite being intrinsically in thermal equilibrium, fluctuations usually completely diminish in a Bose-Einstein condensate soon after the condensation threshold. We measure the second-order coherence of the photon Bose-Einstein condensate to search for the expected ratio of statistical number fluctuations and compressibility following the fluctuation-dissipation theorem. Another intriguing aspect of the photon condensate is introduced due to the imperfect reflectivity of the cavity mirrors. In the second part of this thesis we show that this openness can lead to the existence of new states of the condensate. Physical models often consider systems that are completely isolated from their environment, such as a gas of particles closed in a box. Real-life situations often deviate from these idealized scenarios and the system loses energy or particles to its surroundings. In contemporary physics, systems which are dissipatively coupled to the environment are actively studied in a broad range of research fields ranging from optics to biophysics. Here, we investigate the open-system dynamics of a photon condensate in grand-canonical ensemble conditions. We identify non-Hermitian phases of the system that are observed by abrupt changes in the dynamics of the condensate’s second-order coherence

Yüksek gerilim transformatörlerşnde optimum izolasyon

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Transformatörlerdeki yalıtım sistemlerinin dizaynı temel olarak yalıtım malzemesindeki selülozun transformatör yağı ile kullanımına (etkileşimine) dayanır. Yüzyıldan daha fazla süredir transformatör yalıtım dizaynları ve üretim metotları bu bilgi üzerine temellendirilmiştir. Yalıtım dizaynında yağ ile emprenye edilmiş yalıtım malzemeleri üzerindeki alan dağılımı temel kriter olarak alınmalıdır. Ayrıca yalıtım düzenleri dizayn eğrilerine göre oluşturulurlar. Bu dizayn eğrileri onlarca yıllık tecrübe denemeler testler işçilik kaliteli üretime bağlı olarak çıkarılmıştır..Yağ soğutmalı transformatörlerin imal edilmesi için gerekli hammaddenin giderek azalması, bu materyallerin fiyatlarının pahalı ve dalgalı olması transformatör üreticilerinin maliyetleri, ağırlıkları ve boyutları düşürmek için alternatif çözümler bulmalarını gerekli kılmıştır. Bu tez sargı çıkış düzeneği aracılığıyla sargı çıkış düzeneği dizayn prosesini anlatır. Sargı çıkış düzeneği, yüksek gerilim sargılarının sonlarını geçit izolatörlerinin alt bağlantı noktalarına bağlayan yalıtım parçalarını ve bağlantı elemanlarıdır. Dom çaplarını belirlemek elbette kullanılacak çelik ve mineral yağ miktarını etkileyecektir ve bu tüm transformatörün materyal maliyetleri için önemlidir. Sargı çıkış düzenekleri bu mesafelerin düşürülmesine olanak tanıyıp transformatör üreticilerinin maliyetlerini azaltmıştır.Sargı çıkış düzeneklerinde elektrostatik alan dağılımı çok düzensizdir. Geometriler ve yapılar alan dağılımını optimize edecekmiş gibi düzenlenmelidir. Bu en uygun form için ise geometriler kavramak karşılaştırabilmek gereklidir.Transformatör kartonundan yapılan yalıtım paravanaları geniş yağ kanallarını dar yağ kanallarına bölmek için kullanılır. Transformatör kartonu yağın elektriksel dayanımını arttıran ve daha güvenli sınırlar sağlayan saf selüloz liflerine sahiptir. Dizayn yapılırken önemli nokta Sargı çıkış düzeneği paravanalarının alan uygun yapıda yapılması yani elektrik alan çizgilerine dik eş potansiyel eğrilere paralel yapıda olmasıdır.The general knowledge about transformer Insulation System Design is based on the use of cellulose in insulations which is basically used in mineral oil. For more than one hundred years, transformer design and manufacturing methods are based on this knowledge. In insulation design, field stress distribution between oil impregnated solid insulations is taken as the fundamental criteria. This stress is distributed in accordance with the permittivity of insulating materials and the geometry. Furthermore the insulation arrangement is constituted according to the design curves. They are based on decades of experience and depend upon manufacturing, process, workmanship, quality of materials and so on.Deficiency of materials that are essential for producing oil-cooled transformers, such as Grain Oriented Silicone Steel, Copper, Mineral oil, and their increasing and fluctuating prices necessitate finding alternative solutions to reduce the cost, weight and dimensions of the transformers. This thesis aims to demonstrate optimizing process by means of 'lead exits'. The lead exit is an insulation component and connecting element between high voltage winding end and the bottom of the bushing end. High voltage winding end can be positioned at the top or in the middle of the axial height of the coil. Common practice for each lead system is the phase current through a turret to the bushing bottom end. The turret diameter depends on system voltage and design of the lead exit. Determining of the turret diameter will certainly affect the quantity of steel, mineral oil, etc., and this is important for both material cost and the weight and dimensions of the transformers. Lead exit allows reducing the clearances and the diameter of turret therefore provide saving from materials for power transformer manufacturers.The field stress distribution of such a lead exit is highly non-uniform. The geometries of the structures should be arranged to optimize the field stress distribution. For this optimization, it is necessary to comprehend and compare the geometries.Insulation barriers, made from Transformer board, are used for subdividing large oil gaps into smaller oil gaps. Transformer board has pure cellulose fibers that increase the oil strength and provide a higher safety margin. While designing lead exit barriers the important point is to obtain the 'field conform' structure, i.e. electrical field patterns are perpendicular to barriers and equal potential field patterns are parallel with barriers

BÂKILLÂNİ’NİN MU’TEZİLEYE BAKIŞI (TEMHÎD KİTABI ÖRNEĞİNDE)

Kâdı Bâkıllânî, Eş’arî kelâm geleneğinin sistemleşmesinde ve bir disiplin haline gelmesinde büyük katkıları olmuş müdekkik bir âlimdir. O, Kelâm, Mezhepler Tarihi, Fıkıh Usûlü ve Kur’ân ilmi alanlarında kendisinden sonraki ilim adamlarını etkileyecek düzeyde eserler bırakmıştır. Bu çalışmamızda; müellifin hayatını, ders aldığı hocaları, eserlerini, fikrî dünyasını ve yetiştiği ortamın kültürel yapısını anlatmaya çalıştık. Bunlarla beraber onun Kitâbü Temhîdi’l-Evâ’il ve Telhîsi’d-Delâ’il isimli eserinde Mu’tezile mezhebine getirmiş olduğu eleştirileri, Mu’tezilî bilginlere karşı tavrını ve kendi görüşlerini ele aldık. Örneğin onun, Allah’ın sıfatları, Kur’ân’ın yaratılmışlığı, rü’yetullah, şefâat ve imâmet gibi meselelerde Mu’tezile’ye dair düşüncesinin ne olduğunu ortaya koyduk. Burada Mu’tezile ile Bâkıllânî arasında önemli görüş ayrılıkları olduğunu, bu ayrılığın âyet, hadis ve rivâyetlere bakış açılarının farklı olmasından ve ayrı mezheplere bağlı olmaktan kaynaklandığını ve bu sistematik farklılıkların da inanca dair meselelerdeki görüşlerini etkilediğini tespit ettik

Artificial olfaction with hollow core bragg fiber arrays

Ankara : Materials Science and Nanotechnology Program of The Graduate School of Engineering and Science of Bilkent Univesity, 2014.Thesis (Ph. D.) -- Bilkent University, 2014.Includes bibliographical references leaves 83-89.An optoelectronic nose for the analysis of alcohols (ethanol and methanol) in chemically complex environments is reported. The cross-responsive sensing unit of the optoelectronic nose is an array of three distinct hollow core infrared (IR) transmitting photonic band gap fibers (Bragg fibers), which transmit a specific band of IR light depending on their Bragg mirror structures. Presence of alcohol molecules in the optofluidic core quench the fiber transmissions if there is an absorption band of the analyte overlapping with the transmission band of the fiber. The cumulative response data of the fiber array enables rapid, reversible and accurate discrimination of alcohols in chemically complex backgrounds such as beer and fruit juice. In addition, we observed that humidity of the environment has no effect on the response of the optoelectronic nose, which is rarely achieved in gas sensing applications. Consequently, it can be reliably used in virtually any environment without precalibration for humidity or drying the analytes. To further improve the performance, we engineered the photonic bandgap of Bragg fibers by controlling the thickness profile of the fiber during the thermal drawing. Conical hollow core Bragg fibers were produced by thermal drawing under a rapidly alternating load, which was applied by introducing steep changes to the fiber drawing speed. In conventional cylindrical Bragg fibers, light is guided by omnidirectional reflections from interior dielectric mirrors with a single quarter wave stack period. In conical fibers, the diameter reduction introduced a gradient of the quarter wave stack period along the length of the fiber. Therefore, the light guided within the fiber encountered slightly smaller dielectric layer thicknesses at each reflection, resulting in a progressive blueshift of the reflectance spectrum. As the reflectance spectrum shifts, longer wavelengths of the initial bandgap cease to be omnidirectionally reflected and exit through the cladding, which narrows the photonic bandgap. A narrow transmission bandwidth is particularly desirable in hollow waveguide mid-infrared sensing schemes such as the optoelectronic nose. We carried out sensing simulations using the absorption spectrum of isopropyl alcohol vapor to demonstrate the importance of narrow bandgap fibers in chemical sensing applications.Öztürk, Fahri EmrePh.D

Managing health and safety risks in restoration/renovation of historic buildings

Restoration and renovation of historic buildings aim to preserve and sustain those buildings with their original state. This fact is important to conserve historical values for a society as well as for sustainable city planning. Restoration projects have their own occupational health and safety risks and differ from ordinary construction projects. Additionally, implementation of safety measures according to the current regulations are very difficult due to geometrical structure, type of material used and preservation consideration for the structural and architectural elements of the historic buildings. Since the risks as well as mitigation and abatement techniques differ from conventional buildings, restoration projects require paying attention to establish safety and health plan and risk management system to implement safety and health measures. In this paper, different health and safety risks of the restoration projects are discussed. Different safety and health practices are dealt with ordinary structures, risk assessment is made according to specific risks, findings are revealed in some certain restoration projects in Turkey and a new approach for health and safety management in restoration projects is introduced.Publisher's Versio

Simple Sensor Application: Determination of Electrochemical Properties of Carvedilol in CPE Based on Zinc Oxide Nanoparticles and Development of the Method for its Determination in Pharmaceutical Samples

In the study, the electrochemical characteristics of carvedilol were determined by cyclic voltammetry and square wave voltammetry on carbon paste electrode with zinc oxide nanoparticles at pH 8.0 in Britton Robinson buffer. The adsorption characteristics of the molecule on the modified electrode and the electron number accompanying the electrode reaction were calculated. In addition, a new square wave anodic adsorptive stripping voltammetry process was suggested for the determination of carvedilol drug samples. The linear concentration range and detection limit of the process were found to be 0.07 µM–2.61 µM and 0.09 µM, respectively. Recovery studies of CAR in the pharmaceutical sample were performed to check the accuracy of the developed process. With the developed process, results with high reliability, reproduceability, accuracy and precision were obtained for the determination of CAR in pharmaceutical samples

Baro pullarında yapılan sahteciliğin kıymetli damgada sahtecilik suçu kapsamında değerlendirilip değerlendirilemeyeceği meselesi

En genel tanımıyla suçta ve cezada kanunilik ilkesi, suç teşkil eden fiiller ile bu fiiller karşılığında öngörülen yaptırımların kanunla düzenlenmiş olması anlamını taşır. Türk Ceza Kanunu'nun 199’uncu maddesinde "Kıymetli Damgada Sahtecilik" suçu düzenlenmiştir. Bu suçun konusu olan kıymetli damga kavramı, muayyen bir miktar vergi ya da harcın ödendiğini belgelemek amacıyla kullanılan pulları da kapsar. Türk Hukukunda avukatların vekaletnamelere yapıştırdığı baro pulu gibi bazı pul ve damgalar karşılığında ödenen bedeller vergi veya harç niteliğinde olmayıp, vergi benzeri mali yükümlülük niteliğindedir. Bu çalışmada, karşılığında ödenen bedel itibarıyla vergi benzeri mali yükümlülük niteliğinde olan baro pullarında yapılan sahtecilik eylemlerinin, "Kıymetli Damgada Sahtecilik" suçuna sebebiyet verip vermeyeceği hususu suçta ve cezada kanunilik ilkesi bağlamında değerlendirilmiştir

Siyasi partiler hakkında uygulanan devlet yardımından yoksun bırakma yaptırımının hukuki niteliği

Anayasa’da da ifade edildiği gibi siyasi partiler demokratik siyasi hayatın vazgeçilmez unsurlarıdırlar. Bugün için, siyasi partilerin mevcut olmadığı ve bunların adil bir seçim sistemi ile iktidar yarışına girmediği bir ülkede demokrasinin varlığından bahsedilemez. Ancak siyasi partilerin demokratik siyasi hayat bakımından arz ettiği önem, bunların her hâl ve şart altında faaliyetlerini sürdürebilecekleri anlamına gelmemektedir. Zorunlu bazı hâllerde siyasi partilerin kapatılması demokrasi ilkesini ihlal etmez. Nitekim Anayasa’nın 69’uncu maddesinde siyasi partilerin bazı yasak eylemleri işlemesi kapatılma sebebi olarak öngörülmüştür. Bu maddeye 2001 yılında eklenen bir hüküm ile işlenen fiillerin ağırlığı göz önünde bulundurularak, siyasi partiler hakkında kapatma kararı yerine Devlet yardımından kısmen veya tamamen yoksun bırakma kararı verilebilmektedir. Görüldüğü üzere bu yaptırım parti kapatma yaptırımına bir alternatif olarak öngörülmüştür. Hukukumuzda siyasi parti kapatma kararlarının hukuki niteliği tartışmalı olduğu gibi, bu yaptırıma alternatif olarak öngörülen Devlet yardımından kısmen veya tamamen yoksun bırakma yaptırımının hukuki niteliğinin ne olduğu hususu da aydınlatılmaya muhtaçtır. Çalışmamızda siyasi partiler hakkında uygulanan Devlet yardımından kısmen veya tamamen yoksun bırakma yaptırımının hukuki niteliği analiz edilecektir