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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Chiropractic alters TMS induced motor neuronal excitability: preliminary findings(Springer International Publishing Ag, 2014) Haavik, Heidi; Niazi, Imran Khan; Duehr, Jens; Kinget, Mat; Ugincius, Paulius; Department of Physics; N/A; Sebik, Oğuz; Yılmaz, Gizem; Türker, Kemal Sıtkı; Researcher; PhD Student; Faculty Member; Department of Physics; College of Sciences; Graduate School of Health Sciences; School of Medicine; Koç University Hospital; N/A; N/A; 6741The objective of this study was to use the electromyography (EMG) via surface and intramuscular single motor unit recordings to further characterize the immediate sensorimotor effects of spinal manipulation and a control intervention using TMS. The results provide evidence that spinal manipulation of dysfunctional spinal segments increases low threshold motoneurone excitability.Publication Metadata only Spectroscopic characterization of Tm3+:TeO2-K2O-Nb2O5 glasses for 2- μm lasing applications(Elsevier Science Bv, 2012) Kurt, Adnan; Speghini, Adolfo; Bettinelli, Marco; Department of Physics; Department of Physics; Department of Physics; Görgülü, Adil Tolga; Çankaya, Hüseyin; Sennaroğlu, Alphan; Master Student; Researcher; Faculty Member; Department of Physics; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 23851We have performed detailed experiments to investigate the spectroscopic properties of a new type of tellurite based host doped with thulium: Tm2O3:(0.70)TeO2-(0.15)K2O-(0.15)Nb2O5 having Tm2O3 concentrations of 0.125, 0.25, 0.5, and 1.0 mol%. By performing a Judd-Ofelt analysis of the absorption bands, we obtained average radiative lifetimes of 2.57 +/- 0.20 and 0.35 +/- 0.01 ms for the H-3(4) and F-3(4) levels, respectively. Furthermore, we also observed that an increase in the Tm2O3 concentration from 0.125 to 1.0 mol% results in a decrease of the measured fluorescence lifetime from 814 to 439 mu s and from 258 to 47 mu s for the H-3(4) and F-3(4) levels, respectively, due to efficient non-radiative decay. The highest quantum efficiency of 32% was obtained for the sample doped with 0.125 mol% Tm2O3 for the H-3(4) level. Results show that cross relaxation becomes important as the ion concentration is increased, leading to the quenching of the 1460-nm band and enhancement of the 1860-nm emission. The highest emission cross section of 6.85 x 10(-21) Cm-2 measured for the 1860-nm band reveals the potential of this host for the development of 2-mu m lasers in bulk glass as well as fiber media. (C) 2011 Published by Elsevier B.V.Publication Metadata only Graphene mode-locked Cr:ZnSe laser(Optical Society of America (OSA), 2013) Kim J.W.; Bae S.; Hong B.H.; Rotermund F.; N/A; Department of Physics; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851We report a graphene mode-locked Cr:ZnSe laser which produces femtosecond pulses with duration as short as 176 fs and pulse energy as high as 2.4 nJ at a 78-MHz repetition rate near 2400 nm.Publication Metadata only Optical modulation with silicon microspheres(IEEE-Inst Electrical Electronics Engineers Inc, 2009) Gürlü, Oğuzhan; N/A; Department of Physics; Yüce, Emre; Serpengüzel, Ali; Master Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; 245435; 27855In this letter, a silicon microsphere coupled to a silica optical fiber half coupler has been characterized for electrooptical modulation in the L-band at 1.55 mu m. Electrooptical modulation of the transmitted and the 90 degrees elastic scattered signals for both the TE and the TM polarizations of the microsphere resonances has been observed.Publication Metadata only Investigation of the ultrafast response and saturable absorption of voltage-controlled graphene(Optica Publishing Group (formerly OSA), 2018) Kakenov N.; Kocabas C.; N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; PhD Student; PhD Student; Faculty Member; Department of Physics; 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 Sciences; N/A; N/A; 23851Ultrafast pump-probe measurements show that at a bias voltage of 1V, voltage reconfigurable graphene supercapacitors can operate as fast saturable absorbers with adjustable insertion loss over an ultrabroad spectral range from 630 to 1100 nm.Publication Metadata only Resonant channel-dropping filter with integrated detector system based on optical fiber coupler and microsphere(IOP Publications, 2004) İşci, Şenol; Yılmaz, Yiğit; Department of Physics; Serpengüzel, Ali; Kurt, Adnan; Bilici, Temel; Faculty Member; Teaching Faculty; N/A; Department of Physics; College of Sciences; N/A; 27855; 194455; N/APublication Metadata only Motion of single terrylene molecules in confined channels of poly(butadiene)-poly(ethylene oxide) diblock copolymer(Amer Chemical Soc, 2009) N/A; Department of Physics; Department of Chemistry; Yorulmaz, Mustafa; Kiraz, Alper; Demirel, Adem Levent; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 22542; 6568The motion of terrylene probe molecules in confined PB channels of an asymmetric PB-PEO diblock copolymer has been investigated by single molecule tracking. The one-dimensional diffusion coefficients were found to be significantly smaller and had a narrower distribution compared to two-dimensional diffusion coefficients in PB. The trajectories of some single molecules showed unusual behavior of directed motion where mean square displacement had a parabolic dependence oil lag time. The likely origin of this behavior is discussed in terms of local variations in the PB channel width and the resulting change in the local density. The results show the effect of nonuniformities and heterogeneities in the channels on the motion of single molecules and demonstrate the sensitivity of single molecule tracking in characterizing self-assembled block copolymer morphologies.Publication Metadata only Concentration dependence of the infrared luminescence efficiencies in TEO-CDCL2 : TM3+ glass(Optica Publishing Group, 2003) Özalp, M. Reha; Özen, Gönül; Department of Physics; Department of Physics; Sennaroğlu, Alphan; Kurt, Adnan; Faculty Member; Teaching Faculty; Department of Physics; College of Sciences; College of Sciences; 23851; 194455Using exper imental methods, the characteristics of the 1450-nm and 1800-nm luminescence bands of Tm3+ doped TeO2-CdCl2 glasses were studied as a function of the Tm3+ doping level.Publication Metadata only FRET lasing from self-assembled DNA tetrahedral nanostructures suspended in optofluidic droplet resonators(Springer, 2014) Jonas, A.; Liu, H.; Fan, C.; Chen, Q.; Fan, X.; Department of Physics; N/A; N/A; Kiraz, Alper; Özelci, Ersan; Aas, Mehdi; Faculty Member; PhD Student; PhD Student; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 22542; N/A; N/AWe demonstrate Förster resonance energy transfer (FRET) lasing from self-assembled tetrahedral DNA complexes labeled with Cy3 and Cy5 dyes and suspended as a gain medium in aqueous microdroplet cavities deposited on a superhydrophobic surface. Threshold fluence and differential efficiency are characterized for DNA complexes containing 1Cy3-3Cy5 and 3Cy3-1Cy5. We demonstrate that at a constant Cy5 concentration, average threshold fluence is reduced 3 to 8 times and average differential efficiency is enhanced 6 to 30 times for 3Cy3-1Cy5 as compared to 1Cy3-3Cy5. Using 3Cy3-1Cy5 nanostructures, FRET lasing is observed at very low concentrations down to ∼ 1 μM. This work shows that optofluidic microlasers based on droplet resonators can be combined with DNA nanotechnology to explore applications in bio/chemical sensing and novel photonic devices.Publication Metadata only Mid-infrared elastic scattering from germanium microspheres(IEEE, 2016) N/A; N/A; N/A; N/A; Department of Physics; Zakwan, Muhammad; Bayer, Mustafa Mert; Anwar, Muhammad Sohail; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; PhD Student; Master Student; Master Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 27855Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, especially in the mid-infrared (mid-IR) wavelengths. As a semiconductor material for microphotonics applications [1], germanium is particularly attractive owing to its large nonlinearity, high optical damage threshold compared with traditional nonlinear glass materials, and above all, its broad transparency window, extending from the near-IR into the mid-IR. Germanium based optical components have found numerous applications in imaging systems operating in the mid-IR wavelengths, where the principal natural greenhouse gases do not exhibit strong absorption. These applications include rapid sensing and diagnosis [2,] [3], industrial process controls, environmental monitors to hazardous chemical detection [4]. Germanium also is a good electromagnetic shielding material, an attribute that has become increasingly important for modern military applications, where other signals (within the millimeter and centimeter wavelength range) can be strong enough to interfere with nearby IR systems. Elastic light scattering from a germanium microsphere has already been observed in the near-IR [5]. Here, elastic light scattering from a germanium microsphere in the mid-IR region is numerically analyzed using generalized Lorenz-Mie theory (GLMT) [6]. Light interaction with microspheres of various materials is of much interest because of their photonic properties [7]. Germanium has a refractive index of 4, which is even higher than the refractive index of silicon (3.5) in the mid-IR region. The higher refractive index results in higher quality factor morphology dependent resonances (MDRs). A higher value of Q indicates a longer lifetime of the photons trapped inside the cavity and a narrower MDR. Here, the MDRs are observed numerically in the transverse magnetically (TM) and transverse electrically (TE) polarized 90° elastic scattering and 0° transmission for a 40 µm radius germanium microsphere in the mid-IR wavelengths ranging from 5.4 µm to 5.6 µm [8]. The mode spacing of approximately 41 nm between the resonances with the same radial mode order and consecutive polar mode number shows good correlation with the optical size of the germanium microsphere. The germanium microsphere with its high quality factor MDRs can be suitable for optical monitoring and sensing applications in the mid-IR, which require a high spectral resolution [9].