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Öğe Biosynthesis of silver nanoparticles using leaves of Stevia rebaudiana(Elsevier Science Sa, 2011) Yilmaz, M.; Turkdemir, H.; Kilic, M. Akif; Bayram, E.; Cicek, A.; Mete, A.; Ulug, B.The synthesis of silver nanoparticles employing a shadow-dried Stevia rebaudiana leaf extract in AgNO3 solution is reported. Transmission electron microscopy and X-ray diffraction inspections indicate that nanoparticles are spherical and polydispersed with diameters ranging between 2 and 50 nm with a maximum at 15 nm. Ultraviolet-visible spectra recorded against the reaction time confirms the reduction of silver nanoparticles indicating that the formation and the aggregation of nanoparticles take place shortly after the mixing, as they persist concurrently with characteristic times of 48.5 min and 454.5 min, respectively. Aggregation is found to be the dominant mechanism after the first 73 min. Proton nuclear magnetic resonance spectrum of the silver nanoparticles reveals the existence of aliphatic, alcoholic and olefinic CH2 and CH3 groups, as well as some aromatic compounds but no sign of aldehydes or carboxylic acids. Infrared absorption of the silver nanoparticles suggests that the capping reagents of silver and gold nanoparticles reduced in plant extracts/broths are of the same chemical composition of different ratios. Ketones are shown to play a somehow active role for the formation of nanoparticles in plant extracts/broths. (C) 2011 Elsevier B.V. All rights reserved.Öğe Polarization-Independent Self-Collimated Beam Splitting in Two-Dimensional Photonic Crystals(Ieee Computer Soc, 2012) Yucel, M. B.; Kaya, O. A.; Cicek, A.; Ulug, B.Polarization-independent splitting of self-collimated transverse-electric and transverse-magnetic polarized waves in a two-dimensional square photonic crystal are demonstrated. The beam splitting is facilitated by the existence of sharp edges in flat equifrequency contours.Öğe Self-collimation and slow-sound effect of spoof surface acoustic waves(Amer Inst Physics, 2019) Korozlu, N.; Kaya, O. A.; Cicek, A.; Ulug, B.Self-collimated propagation and slow-sound effect of spoof acoustic surface waves over a thin solid slab with partially embedded spherical cavities in a square lattice are numerically and experimentally demonstrated. Band structure calculations via the Finite-Element Method reveal that a single spoof surface wave band appears below the air-line, which flattens as the spheres are embedded deeper, leveraging the observation of self-collimated slow spoof modes. For a radius-to-lattice constant ratio of 0.45 and embedding depth of 60% of the radius, the surface band is such that non-diffractive guiding of spoof waves along the [11] direction can be achieved. Persistent self-collimated propagation of spoof surface waves over long distances is demonstrated through frequency-domain Finite-Element Method simulations. Plane waves incident from air can couple to the self-collimated modes for a wide range of azimuthal angle of incidence up to 60 degrees, where the polar angle of incidence can be in the range of +/- 15 degrees. Self-collimation of spoof waves is experimentally realized by employing a plane-wave source incident from air. In addition, when the embedding depth is higher than 85%, self-collimated slow spoof modes with group indices higher than 15 can be obtained. The observed phenomena can be utilized in two-dimensional acoustic systems such as logic circuits and interferometric sensing devices. Published under license by AIP Publishing.
