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Publication Metadata only “O/F shift” in hybrid rockets(American Institute of Aeronautics and Astronautics, 2014) Toson, Elena; Evans, Brian; Department of Mechanical Engineering; Karabeyoğlu, Mustafa Arif; Faculty Member; Department of Mechanical Engineering; College of Engineering; 114595For most hybrid rocket systems, oxidizer to fuel ratio (O/F) changes over time due to 1) natural growth of the fuel port diameter and 2) oxidizer flow rate variations, if throttling is employed. This phenomenon, which is referred to as “O/F shift”, leads to a reduction in motor performance. Note that liquid or solid rocket motors are not subject to temporal O/F variations, which is wrongfully considered as one of the most critical disadvantages of hybrid rockets. In this paper, the effect of “O/F shift” is quantified for hybrid rocket motors. Analytical formulas for the temporal O/F variation and the overall c* efficiency drop associated with the variation has been derived for single circular port motors. It has been shown that for a typical motor, c* efficiency drop due to O/F variation is well below 0.2%, a value which is too small to be measured in an actual motor test. It is also shown that for a wagon wheel type multiport configuration (with triangular ports), efficiency drop is significantly worse than the single circular port case. Even for the multiport systems, the shift does not have a controlling effect on the overall efficiency of the motor. A number of strategies have been outlined to control the adverse effects of O/F variation in a hybrid rocket. For a single circular port design with limited throttling, no mitigation is required. For systems with deep throttling requirements, aft oxidizer injection seems like a viable strategy to retain a high level of overall efficiency.Publication Metadata only 1.07 - Rubberlike elasticity(Elsevier, 2012) Mark, J.E.; Department of Chemical and Biological Engineering; Erman, Burak; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 179997Molecular structure, molecular and phenomenological theories, and computer simulations of amorphous rubberlike polymeric networks of rubber elasticity are discussed. Behavior of responsive gels, multimodal, liquid-crystalline, and reinforced elastomers in the state of thermodynamic equilibrium are outlined. Characterization of structure and properties based on stress–strain experiments, optical and spectroscopic techniques, scanning tunneling microscopy, atomic force microscopy, nuclear magnetic resonance, small-angle and Brillouin scattering, and pulse wave propagation are outlined. © 2012 Elsevier B.V. All rights reserved.Publication Metadata only 16.4: the optics of an autostereoscopic multiview display(SID, 2010) Baghsiahi, Hadi; Selviah, David R.; Willman, Eero; Fernández, Anibal; Day, Sally E.; Surman, Phil A.; N/A; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Erden, Erdem; Chellappan, Kishore Velichappattu; Ürey, Hakan; Master Student; Researcher; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 8579An autostereoscopic head-tracked back projection display that uses an RGB laser illumination source and a fast light engine is described. Images are horizontally scanned columns controlled by a spatial light modulator that directs two or more images in the directions of the apposite viewers 'eyes.Publication Metadata only 3D bioprinted glioma models(Iop Publishing Ltd, 2022) N/A; N/A; N/A; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Yığcı, Defne; Sarabi, Misagh Rezapour; Üstün, Merve; Atçeken, Nazente; Sokullu, Emel; Önder, Tuğba Bağcı; Taşoğlu, Savaş; Undergraduate Student; PhD Student; PhD Student; Researcher; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); School of Medicine; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; School of Medicine; School of Medicine; College of Engineering; N/A; N/A; N/A; N/A; 163024; 184359; 291971Glioma is one of the most malignant types of cancer and most gliomas remain incurable. One of the hallmarks of glioma is its invasiveness. Furthermore, glioma cells tend to readily detach from the primary tumor and travel through the brain tissue, making complete tumor resection impossible in many cases. To expand the knowledge regarding the invasive behavior of glioma, evaluate drug resistance, and recapitulate the tumor microenvironment, various modeling strategies were proposed in the last decade, including three-dimensional (3D) biomimetic scaffold-free cultures, organ-on-chip microfluidics chips, and 3D bioprinting platforms, which allow for the investigation on patient-specific treatments. The emerging method of 3D bioprinting technology has introduced a time- and cost-efficient approach to create in vitro models that possess the structural and functional characteristics of human organs and tissues by spatially positioning cells and bioink. Here, we review emerging 3D bioprinted models developed for recapitulating the brain environment and glioma tumors, with the purpose of probing glioma cell invasion and gliomagenesis and discuss the potential use of 4D printing and machine learning applications in glioma modelling.Publication Metadata only 3D object matching via multivariate shape distributions(Institute of Electrical and Electronics Engineers (IEEE), 2005) Akgül, C.B.; Sankur, B.; Schmitt, F.; Department of Computer Engineering; Yemez, Yücel; Faculty Member; Department of Computer Engineering; College of Engineering; 1079073B nesne eşleştirme literatüründe, problemi şekil dağılımlarının karşılaştırılmasına indirgeyen yöntemler bulunmaktadır. Şekil dağılımı, 3B nesne yüzeyi üzerinde hesaplanan bir işlevin değerlerinin olasılık dağılımı olarak tanımlanır. Bu çalışmada varolan yöntemi, birden çok işlevin getirdiği şekil bilgisinden aynı anda yararlanacak şekilde genişletiyoruz. Çokboyutlu şekil dağılımları adını verdiğimiz bu 3B nesne betimleyicilerini, örnek bir 3B nesne veri tabanındaki nesneler için parametrik olmayan yaklaşımlarla kestiriyor, karşılaştırmaları alternatif metrikler yoluyla yapıyoruz. Elde edilen kesinlik-geri getirme eğrileri çokboyutlu şekil dağılımlarının karşılaştırılmasının yeni bir 3B nesne eşleştirme paradigması olabileceğini göstermektedir.Publication Open Access 3D-printed contact lenses: challenges towards translation and commercialization(Future Medicine, 2022) Yetişen, Ali K.; Department of Mechanical Engineering; Taşoğlu, Savaş; Özdalgıç, Berin; Faculty Member; PhD Student; Department of Mechanical Engineering; KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; Graduate School of Sciences and Engineering; 291971; 323683NAPublication Open Access 3D-printed multi-stimuli-responsive mobile micromachines(American Chemical Society (ACS), 2020) Lee, Yun-Woo; Ceylan, Hakan; Yasa, İmmihan Ceren; Department of Mechanical Engineering; Kılıç, Uğur; Sitti, Metin; Faculty Member; Department of Mechanical Engineering; School of Medicine; College of EngineeringMagnetically actuated and controlled mobile micromachines have the potential to be a key enabler for various wireless lab-on-a-chip manipulations and minimally invasive targeted therapies. However, their embodied, or physical, task execution capabilities that rely on magnetic programming and control alone can curtail their projected performance and functional diversity. Integration of stimuli-responsive materials with mobile magnetic micromachines can enhance their design toolbox, enabling independently controlled new functional capabilities to be defined. To this end, here, we show three-dimensional (3D) printed size-controllable hydrogel magnetic microscrews and microrollers that respond to changes in magnetic fields, temperature, pH, and divalent cations. We show two-way size-controllable microscrews that can reversibly swell and shrink with temperature, pH, and divalent cations for multiple cycles. We present the spatial adaptation of these microrollers for penetration through narrow channels and their potential for controlled occlusion of small capillaries (30 μm diameter). We further demonstrate one-way size-controllable microscrews that can swell with temperature up to 65% of their initial length. These hydrogel microscrews, once swollen, however, can only be degraded enzymatically for removal. Our results can inspire future applications of 3D- and 4D-printed multifunctional mobile microrobots for precisely targeted obstructive interventions (e.g., embolization) and lab- and organ-on-a-chip manipulations.Publication Metadata only 48.4: Beam forming for a laser based auto-stereoscopic multi-viewer display(Blackwell Publishing Ltd, 2011) Baghsiahi, Hadi; Selviah, David R.; Willman, Eero; Fernández, Anibal; Day, Sally E.; Surman, Phil A.; N/A; Department of Electrical and Electronics Engineering; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Akşit, Kaan; Ölçer, Selim; Mostafazadeh, Aref; Erden, Erdem; Chellappan, Kishore Velichappattu; Ürey, Hakan; PhD Student; Other; N/A; Other; N/A; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; College of Engineering; N/A; N/A; N/A; N/A; N/A; 8579An auto-stereoscopic back projection display using a RGB multiemitter laser illumination source and micro-optics to provide a wider view is described. The laser optical properties and the speckle due to the optical system configuration and its diffusers are characterised. © 2011 SID.Publication Metadata only [BMIM][OAc] coating layer makes activated carbon almost completely selective for CO2(Elsevier Science Sa, 2022) N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Durak, Özce; Zeeshan, Muhammad; Keskin, Seda; Uzun, Alper; Master Student; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 40548; 59917Tuning the molecular affinity of porous materials towards desired gases is important to achieve superior selectivity for a target separation. Herein, we report a novel composite, prepared by coating an ordinary activated carbon (AC) with an ionic liquid (IL) (1-butyl-3-methylimidazolium acetate, [BMIM][OAc]) offering an almost complete CO2 selectivity over N-2 and CH4. Data indicated that pore blockage by the IL accompanied with the enhancement in polarity and reduction in the hydrophobic character of the surface hindered the sorption of N-2 and CH4. For CO2, on the other hand, new chemisorption and physisorption sites became available associated with the IL layer on the surface, making the composite material significantly selective. Newly formed chemisorption sites attributed to the cation's acidic C2H sites, which become available with bi-layer formation. Presence of multiple competitive sorption sites with different energies was further proven with thermal analysis and detailed spectroscopic analysis. Data showed that CO2/CH4 and CO2/N-2 ideal selectivities boosted from 3.3 to 688.3 (2.3 to 54.7) and from 15.6 to 903.7 (7.1 to 74.3) at 0.1 (1) bar and 25 degrees C, respectively, upon the deposition of IL layer. Especially at lower pressures, the IL/AC material became almost fully selective for CO2 offering ideal selectivities in the order of several tens of thousands. To the best of our knowledge, the remarkable enhancement in the ideal CO2 selectivity by a straightforward post-synthesis modification of an ordinary AC, as reported here, sets a new benchmark in high-performance and efficient gas separation for similar porous materials.Publication Open Access A 2D MEMS stage for optical applications(Society of Photo-optical Instrumentation Engineers (SPIE), 2006) Ataman, Çağlar; Petremand, Yves; Noell, Wilfried; Epitaux, Marc; de Rooij, Nico F.; Department of Electrical and Electronics Engineering; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 8579A 2D MEMS platform for a microlens scanner application is reported. The platform is fabricated on an SOI wafer with 50/μm thick device layer. Entire device is defined with a single etching step on the same layer. Through four S-shaped beams, the device is capable of producing nonlinear 2D motion from linear ID translation of two pairs of comb actuator sets. The device has a clear aperture of 2mm by 2mm, which is hallowed from the backside for micro-optics assembly. In this paper, a numerical device model and its validation via experimental characterization results are presented. Integration of the micro-optical components with the stage is also discussed. Additionally, a new driving scheme to minimize the settling time of the device in DC operation is explored.