Browsing by Subject "Rotation"

Now showing 1 - 7 of 7

Open Access
Algorithms for layout of disconnected graphs
(Elsevier, 2000) Doğrusöz, Uğur
We present efficient algorithms for the layout of disconnected objects in a graph (isolated nodes and components) for a specified aspect ratio. These linear and near-linear algorithms are based on alternate-bisection and two-dimensional packing methodologies. In addition, the parameters that affect the performance of these algorithms as well as the circumstances under which the two methodologies perform well are analyzed.
Open Access
Design and determination of stator geometry for axial flux permanent magnet free rod rotor synchronous motor
(2011) Kalender O.; Ege, Y.; Nazlibilek, S.
During designing a new axial flux permanent magnet free rod rotor synchronous motor, it is important to know before hand in which phase the largest angular velocity can occur, what is the ways to reduce the power consumption, how to achieve to increase or decrease the rotation speed by changing the core geometry. Therefore, presenting these preliminary information that are necessary for the design of a free rod rotor synchronous motor to the researchers is the aim of this work. In this respect, this study presents the design and geometrical dimensions of the stator for a new synchronous motor which is an axial flux permanent magnet free rod machine with three, four, five and six phases. This type of motors are an innovative approach especially for the applications used in industrial stirrers. Each type of stator is designed such that it has an appropriate number of phases. The rotating magnetic field over the stator is established by a PIC based microcontroller feeding the interface circuit to the stator wounds. The maximum angular speeds of bar magnet rotors with four different lengths and masses are calculated theoretically and determined experimentally. In addition, the effects of the distance between the rotor and stator, the angular speed of the rotor within the limits of the operation, and the volume of the liquid to be stirred to the power applied are investigated. Furthermore, the effects of the lengths and angular speeds of the bar magnet rotors to the distance between the rotor and stator are determined. In the light of the information obtained and taking into account the power used, the most appropriate parameters and variables such as the stator geometry changing with the phase used, the length of rotor, the distance between the rotor and stator and the angular speeds of rotor are determined. © 2011 Elsevier Ltd. All rights reserved.
Open Access
P band in a rotating optical lattice
(The American Physical Society, 2008) Umucalılar, R. O.; Oktel, M. Ö.
We investigate the effects of rotation on the excited bands of a tight-binding lattice, focusing particularly on the first excited (p) band. Both the on-site energies and the hopping between lattice sites are modified by the effective magnetic field created by rotation, causing a nontrivial splitting and magnetic fine structure of the p band. We show that Peierls substitution can be modified to describe p band under rotation, and use this method to derive an effective Hamiltonian. We compare the spectrum of the effective Hamiltonian with a first-principles calculation of the magnetic band structure and find excellent agreement, confirming the validity of our approach. We also discuss the on-site interaction terms for bosons and argue that many-particle phenomena in a rotating p band can be investigated starting from this effective Hamiltonian.
Open Access
Photonic band gap via quantum coherence in vortex lattices of Bose-Einstein condensates
(The American Physical Society, 2005) Müstecaplioǧlu, O. E.; Oktel, M. Ö.
We investigate the optical response of an atomic Bose-Einstein condensate with a vortex lattice. We find that it is possible for the vortex lattice to act as a photonic crystal and create photonic band gaps, by enhancing the refractive index of the condensate via a quantum coherent scheme. If high enough index contrast between the vortex core and the atomic sample is achieved, a photonic band gap arises depending on the healing length and the lattice spacing. A wide range of experimentally accessible parameters are examined and band gaps in the visible region of the electromagnetic spectrum are found. We also show how directional band gaps can be used to directly measure the rotation frequency of the condensate.
Open Access
Reconfigurable nested ring-split ring transmitarray unit cell employing the element rotation method by microfluidics
(Institute of Electrical and Electronics Engineers, 2015) Erdil, E.; Topalli, K.; Esmaeilzad, N. S.; Zorlu, O.; Kulah, H.; Aydin, C. O.
A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ring-split ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360° linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.
Open Access
Süslemede simetrinin etkisi
(Gazi Eğitim Fakültesi, 2016) Aktaş, M.; Aktaş, S.; Aktaş, B. K.; Aktaş, Burcu
Süsleme (tessellation); latince tessela (antik Roma mozaiklerinde kullanılan küçük fayans yada köşeli taşa verilen ad) kelimesinden gelmektedir. Britton, Seymor (1989) çalışmasında, süsleme, bir ya da daha fazla biçimde yapılmış, hiç boşluk kalmadan ve çakışma olmadan yüzeyi tamamen kaplayan bir desen olarak tanımlanmış, süslemeler iki boyutlu veya üç boyutlu da olabileceğini ve üç boyutlu süslemeler boşluğu kaplar iken iki boyutlu süslemeler yüzeyi kapladığını ifade etmişlerdir. Süsleme yapılırken farklı teknikler kullanılmaktadır. Bu tekniklerin içinde simetri çeşitlerinin kullanıldığı görülmektedir. Simetri; sanatçıların, mimarların ve bilim adamlarının bir çalışmadaki ahenkli düzeninde, bir heykelde, bir yapıda veya kristaller gibi doğa harikalarında ya da bitki, hayvan formlarında görülmektedir. Matematiğin bütününe bakıldığında da birçok alanda simetri kavramıyla karşılaşmak mümkündür. Field, Golubitsky (2009)'e göre simetri bir yaklaşımdır. Bu çalışmada orijinal çizimler kullanılarak; simetrinin çeşitleri, süsleme tekniklerinin (simetri çeşitleri ile) örnekleri verilmiş, simetri çeşitleri ile örüntü oluşturulup teknikleri nasıl uygulanacağı süslemenin nasıl oluşturulabileceği gösterilmiştir. Bu çalışma ile simetri ve süsleme sanatına yeni bir bakış getirilmiş olup ilgili literatüre yeni bir katkıda da bulunulmuştur.
Open Access
Trapped fermi gases in rotating optical lattices: realization and detection of the topological hofstadter insulator
(The American Physical Society, 2008) Umucalilar, R. O.; Zhai, H.; Oktel, M. Ö.
We consider a gas of noninteracting spinless fermions in a rotating optical lattice and calculate the density profile of the gas in an external confinement potential. The density profile exhibits distinct plateaus, which correspond to gaps in the single particle spectrum known as the Hofstadter butterfly. The plateaus result from insulating behavior whenever the Fermi energy lies within a gap. We discuss the necessary conditions to realize the Hofstadter insulator in a cold atom setup and show how the quantized Hall conductance can be measured from density profiles using the StÅ™eda formula.