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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3

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Sponsors: search.filters.sponsors.TÜBİTAKSubject: search.filters.subject.Applied physics

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Now showing 1 - 5 of 5
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    Anticorrosion efficiency of ultrasonically deposited silica coatings on titanium
    (Elsevier Science Bv, 2013) N/A; N/A; Department of Chemistry; N/A; Ertan, Fatoş Sibel; Kaş, Recep; Miko, Annamaria; Birer, Özgür; Master Student; Master Student; Teaching Faculty; Researcher; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; 163509; N/A
    We utilized high intensity ultrasound to prepare coatings of silica and organically modified silica composed of multiple layers of densely packed nanoparticles. Ultrasound was used to collide nanoparticles onto an activated titanium surface with high speed. Large areas could be homogeneously coated by this method. These coatings were characterized by spectroscopy and microscopy methods and the anticorrosion efficiency in NaCl solution was evaluated by electrochemical measurements. The results indicated that the composite coatings provided good quality barrier layer on bare titanium and decreased the anodic corrosion rate. It was found that increase in the organic content of the coating shifted the passivation potential towards more positive direction. The comparison of the impedance results recorded at the corrosion potential pointed out that in each case a good quality barrier layer was formed on the titanium surface. The outstanding corrosion resistance of the composite coatings with only similar to 200 nm thickness shows that ultrasound assisted deposition can be a competitive method to obtain corrosion protective layers. (c) 2013 Elsevier B.V. All rights reserved.
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    Energy-efficient data transmission for capacitive-coupled human body communication systems
    (Ieee-Inst Electrical Electronics Engineers Inc, 2021) Filipovic, Luka; Herceg, Marijan; Vlaovic, Jelena; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 149116
    In this letter, an energy-efficient and low-complexity method for capacitive-coupled human body communication (CC-HBC) systems is proposed. In the proposed method, called impedance shift keying CC-HBC, the change of impedance between the transmitter's signal and the ground electrode is used to map information. In particular, the transmitter changes the condition of an electrical field generated by the receiver by changing the impedance between its signal and ground electrodes. Subsequently, by detecting the changes in the electric field, the receiver can demodulate the information sent by the transmitter. The CC-HBC channel is obtained using the transfer function method, while the performance of the proposed scheme is compared with frequency shift keying and on-off keying modulations.
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    Residual stress gradients in electroplated nickel thin films
    (Elsevier Science Bv, 2015) N/A; N/A; Department of Chemistry; Department of Mechanical Engineering; Kılınç, Yasin; Ünal, Uğur; Alaca, Burhanettin Erdem; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; 42079; 115108
    Residual stress gradients in electroplated nickel films of 1 mu m thickness are characterized for a wide range of current densities (1-20 mA/cm(2)) and electroplating temperatures (30-60 degrees C) in a nickel sulfamate bath. Although a variety of stress measurements is available, exploration of stress gradients remain unstudied at the scale of 1 mu m. Stress gradients - unlike uniform stresses - can cause significant bending even in monolayered released structures. Moreover, examples of misinterpretation of wafer curvature data as a measure of stress gradients exist in the literature. Based on these motivations, monolayered Ni microcantilevers are employed in this work as mechanical transducers for the characterization of stress gradients within the nickel film. Experiments are supported with finite element simulations. Residual stress gradient is found to vary in the range of about 130 to 70 MP/mu m with the sign change indicating a transition from downward to upward deflection of the microcantilever. Thus, a window of electroplating parameters is established yielding zero residual stress gradients, i.e. straight cantilevers, without the use of any additive agents.
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    Dynamic modeling of soft magnetic film actuated scanners
    (IEEE-Inst Electrical Electronics Engineers Inc, 2009) N/A; N/A; Department of Electrical and Electronics Engineering; Işıkman, Serhan Ömer; Ürey, Hakan; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579
    Dynamic behavior of magnetic thin film actuators is investigated in detail and applied to various laser scanning applications. Magnetic hysteresis effects are incorporated into the model developed in the prior work, which assumes linear magnetization as a function of magnetic field and is based on the distributed point-by-point calculation of the magnetostatic moments and forces across the film surface. A simple functional form is used to model the major B-H loop of ferromagnetic films. The model is validated with permalloy (Ni-Fe) plated polymer actuators. The actuators are excited using an external electro-coil and the structures deflect due to magnetic anisotropy torque. The ac deflection of the actuators is modeled by calculating the point-by-point moments on the magnetic film and the solution can handle nonuniform external field and unsaturated magnetic film cases. A 25 degrees optical scan angle is demonstrated for laser scanning display and imaging applications with a nonoptimum coil. Scaling the model to MEMS devices is also discussed.
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    Operation of femtosecond Kerr-lens mode-locked Cr:ZnSe lasers with different dispersion compensation methods
    (Springer, 2012) Kurt, ADNAn; N/A; N/A; Department of Physics; Çizmeciyan, Melisa Natali; Çankaya, Hüseyin; Sennaroğlu, Alphan; PhD Student; Researcher; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 23851
    We employed various low-cost dispersion compensation methods to generate femtosecond pulses from a Kerr-lens mode-locked (KLM) Cr:ZnSe laser operating near 2400 nm. Prism pairs made of CaF2 and MgF2 and slabs of BK7 and YAG were tested. Pulses as short as 92 fs were obtained when a CaF2 prism pair was used in the resonator with a 1% output coupler. With a 6% output coupler and CaF2 prism pair, pulse energies as high as 1.8 nJ were obtained. The KLM operating point was further analyzed for different dispersion compensation scenarios by using the soliton area theorem to determine the nonlinear refractive index (n(2)) of Cr: ZnSe. Results gave an n(2) value of (1.2 +/- 0.2) x 10(-18) m(2)/W in agreement with previous reports.