Browsing by Subject "Operation"

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Cumhuriyet Bayramı kutlamalarına gölge düşüren olay: Adana-Ankara uçağının kaçırılması (29 Ekim 1998)
(Bilkent University, 2020) Bektaş, Ömer Bahadır; Bozdağ, Berk; Özer, Deniz Alp; Çoban, Ertuğrul; Özer, Asya Doğa
29 Ekim 1998'de PKK terör örgütüne mensup olduğu belirlenen Erdal Aksu AdanaAnkara seferini yapmak üzere olan Boeing 737 tipi yolcu uçağını kaçırmıştır. Aynı zamanda Türkiye Cumhuriyeti'nin de 75. Yılına denk gelen bu olay bütün kutlamalara ve de etkinliklere gölge düşürmüştür. Uçağa güvenlik açıklarından faydalanarak bir silah ve bir el bombası sokmayı başaran Erdal Aksu, pilotu uçağı Türkiye Cumhuriyeti adına önemli bir şehir olan Lozan'a indirmesi yönünde zorlamıştır ve burada PKK adına bir bildiri okumak istemiştir. Fakat Ankara Emniyet müdürlüğü ve özel harekât timinin düzenlediği başarılı operasyonlar sayesinde Erdal Aksu amacına ulaşamadan etkisiz hale getirilmiştir. Bu olay havalimanındaki güvenlik açıklarını ortaya çıkarmıştır. Bu kapsamda havalimanları güvenliği artırılmış ve bir daha böyle bir olayın yaşanmaması için önlemler alınmıştır .
Open Access
High Power CMUTs: design and experimental verification
(IEEE, 2012) Yamaner, F. Y.; Olcum, S.; Oguz, H. K.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (CMUTs) have great potential to compete with piezoelectric transducers in high-power applications. As the output pressures increase, nonlinearity of CMUT must be reconsidered and optimization is required to reduce harmonic distortions. In this paper, we describe a design approach in which uncollapsed CMUT array elements are sized so as to operate at the maximum radiation impedance and have gap heights such that the generated electrostatic force can sustain a plate displacement with full swing at the given drive amplitude. The proposed design enables high output pressures and low harmonic distortions at the output. An equivalent circuit model of the array is used that accurately simulates the uncollapsed mode of operation. The model facilities the design of CMUT parameters for high-pressure output, without the intensive need for computationally involved FEM tools. The optimized design requires a relatively thick plate compared with a conventional CMUT plate. Thus, we used a silicon wafer as the CMUT plate. The fabrication process involves an anodic bonding process for bonding the silicon plate with the glass substrate. To eliminate the bias voltage, which may cause charging problems, the CMUT array is driven with large continuous wave signals at half of the resonant frequency. The fabricated arrays are tested in an oil tank by applying a 125-V peak 5-cycle burst sinusoidal signal at 1.44 MHz. The applied voltage is increased until the plate is about to touch the bottom electrode to get the maximum peak displacement. The observed pressure is about 1.8 MPa with −28 dBc second harmonic at the surface of the array.
Open Access
Nanometer-scale patterning and individual current-controlled lithography using multiple scanning probes
(A I P Publishing LLC, 1999-06) Wilder, K.; Soh, H. T.; Atalar, Abdullah; Quate, C. F.
Scanning probe lithography (SPL) is capable of sub-30-nm-patterning resolution and nanometer-scale alignment registration, suggesting it might provide a solution to the semiconductor industry’s lithography challenges. However, SPL throughput is significantly lower than conventional lithography techniques. Low throughput most limits the widespread use of SPL for high resolution patterning applications. This article addresses the speed constraints for reliable patterning of organic resists. Electrons field emitted from a sharp probe tip are used to expose the resist. Finite tip-sample capacitance limits the bandwidth of current-controlled lithography in which the tip-sample voltage bias is varied to maintain a fixed emission current during exposure. We have introduced a capacitance compensation scheme to ensure continuous resist exposure of SAL601 polymer resist at scan speeds up to 1 mm/s. We also demonstrate parallel resist exposure with two tips, where the emission current from each tip is individually controlled. Simultaneous patterning with multiple tips may make SPL a viable technology for high resolution lithography.