Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article A Metric for Gravitational Collapse Around a Schwarzschild Black Hole(World Scientific Publishing, 2023) Erdem, Recai; Demirkaya, Betül; Gültekin, KemalWe consider the problem of gravitational collapse of a fluid under the effect of a small Schwarzschild black hole (e.g. a primordial one). We assume the fluid initially may be approximated by a uniform homogeneous dust. Starting from this configuration we obtain a class of metrics under some physically justified assumptions. We find that the metric we obtain includes the dust collapse as a subcase. After discussing some basic properties of the solution, we discuss the case of dust collapse in more detail. We find that the radial and tangential pressures outside the horizon may take positive or negative values depending on the values of the parameters.Article Citation - WoS: 3Citation - Scopus: 3Compact Multilayer Thin-Film Color Filters and Direct Integration on White-Light Diodes for Color Conversion(Optical Society of America, 2021) Yiğen, Serap; Ekmekçioğlu, Merve; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, LütfiWe present highly efficient green, yellow, and red filters based on a metal-dielectric structure. The filters encompass only five layers of alternating zinc tin oxide and silver thin films that are grown on soda lime glass and white light-emitting diodes (LEDs) using direct current magnetron sputtering at room temperature. The designed filters provide efficient color filtering in the visible spectrum. High purity colored light is obtained by direct application of filters on LEDs as color converters. The presented method offers an easy way for realizing different colors by tuning the thicknesses of layers in the structure. (C) 2021 Optical Society of AmericaBook Part Citation - Scopus: 1Thz Sources and Detectors Fabricated From High Temperature Superconductors(Springer, 2021) Demirhan, Yasemin; Türkoğlu, Fulya; Altan, Hakan; Sabah, Cumali; Özyüzer, LütfiHigh temperature superconductors have unique properties that can be useful in the THz region, single crystal constituted from superconducting CuO2-layers could sustain high voltages across the junctions and they are coupled through the intrinsic Josephson Effect this maintains the potential for very intense, coherent radiation which spreads over the THz gap. We investigated various experimental techniques to fabricate THz sources, bolometers and filters for efficient THz emission and detection. Rectangular mesa structures were fabricated on Bi2Sr2CaCu2O8-x (Bi2212) single crystal superconductors using standard e-beam lithography and Ar ion beam etching systems and an emitted power as high as 60 ?W at frequencies up to 0.85 THz was detected from micron sized continuous wave terahertz sources. We also fabricated bolometric microchips for THz detection purpose from Bi2212 single crystals. Bi2212 microchips detected the signals and response time were calculated, our results have clearly shown that Bi2212 single crystals are potential candidates for THz detection. The detection properties and sensitivity of bolometer chips can be further improved by integrating an antenna and filter structures. In order to investigate this we have fabricated metamaterial THz filters based on metals and YBa2Cu3Ox superconducting thin films with metal-mesh shape and a unique fourcross shape pattern. Both a THz time domain spectrometer and a Fourier transform infrared spectrometer (FTIR) were used to investigate the performance of these filters and the results were compared with simulations done with a commercially available electromagnetic simulation software. © Springer Nature B.V. 2021.Article Citation - WoS: 14Citation - Scopus: 32Search for Physics Beyond the Standard Model in Opposite-Sign Dilepton Events in Pp Collisions at Root S=7 Tev(Springer Verlag, 2011) Karapınar, Güler; Demir, Durmuş AliA search is presented for physics beyond the standard model (SM) in final states with opposite-sign isolated lepton pairs accompanied by hadronic jets and missing transverse energy. The search is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 34 pb(-1). No evidence for an event yield beyond SM expectations is found. An upper limit on the non-SM contribution to the signal region is deduced from the results. This limit is interpreted in the context of the constrained minimal supersymmetric model. Additional information is provided to allow testing the exclusion of specific models of physics beyond the SM.Article Citation - WoS: 14Citation - Scopus: 50Search for Supersymmetry in Events With a Lepton, a Photon, and Large Missing Transverse Energy in Pp Collisions at Root S=7 Tev(Springer Verlag, 2011) Karapınar, Güler; Demir, Durmuş AliA search is performed for an excess of events, over the standard model expectations, with a photon, a lepton, and large missing transverse energy in pp collisions root s = 7TeV. Such events are expected in many new physics models, in particular a theory that is broken via a gauge-mediated mechanism, when the lightest and neutral gauginos are mass degenerate. The data sample used in this search to an integrated luminosity of 35 pb(-1) collected with the CMS detector at the No evidence of such an excess above the standard model backgrounds, dominated by production, is found. The results are presented as 95% confidence level upper limits on the cross section for a benchmark gauge-mediated scenario, and are then converted into exclusion limits on the squark, gluino, and wino masses.Article Citation - WoS: 39Citation - Scopus: 45Search for Same-Sign Top-Quark Pair Production at Root S=7 Tev and Limits on Flavour Changing Neutral Currents in the Top Sector(Springer Verlag, 2011) Karapınar, Güler; Demir, Durmuş AliAn inclusive search for same-sign top-quark pair production in pp collisions at root s = 7 TeV is performed using a data sample recorded with the CMS detector in 2010, corresponding to an integrated luminosity of 35 pb(-1). This analysis is motivated by recent studies of p (p) over bar -> t (t) over bar reporting mass-dependent forward-backward asymmetries larger than expected from the standard model. These asymmetries could be due to Flavor Changing Neutral Currents (FCNC) in the top sector induced by t -channel exchange of a massive neutral vector boson (Z'). Models with such a Z' also predict enhancement of same-sign top-pair production in pp or pp collisions. Limits are set as a function of the Z' mass and its couplings to u and t quarks. These limits disfavour the FCNC interpretation of the Tevatron results.Article Citation - WoS: 102Citation - Scopus: 120Dependence on Pseudorapidity and on Centrality of Charged Hadron Production in Pbpb Collisions at Root S(nn)=2.76 Tev(Springer Verlag, 2011) Karapınar, Güler; Demir, Durmuş AliA measurement is presented of the charged hadron multiplicity in hadronic PbPb collisions, as a function of pseudorapidity and centrality, at a collision energy of 2.76 TeV per nucleon pair. The data sample is collected using the CMS detector and a minimum-bias trigger, with the CMS solenoid off. The number of charged hadrons is measured both by counting the number of reconstructed particle hits and by forming hit doublets of pairs of layers in the pixel detector. The two methods give consistent results. The charged hadron multiplicity density, dN(ch)/d eta vertical bar(eta=0), for head-on collisions is found to be 1612 +/- 55, where the uncertainty is dominated by systematic effects. Comparisons of these results to previous measurements and to various models are also presented.Article Citation - WoS: 52Citation - Scopus: 61Measurement of the Zz Production Cross Section and Search for Anomalous Couplings in 2l2l' Final States in Pp Collisions at Root S=7 Tev(Springer Verlag, 2013) Karapınar, Güler; Demir, Durmuş AliA measurement is presented of the ZZ production cross section in the ZZ -> 2l2l' decay mode with l = e, mu and l' = e, mu, tau in proton-proton collisions at root s = 7 TeV with the CMS experiment at the LHC. Results are based on data corresponding to an integrated luminosity of 5.0 fb(-1). The measured cross section sigma(pp -> ZZ) = 6.24(-080)(+0.86) (stat.)(-0.32)(+0.41) (syst.) +/- 0.14 (lumi.) pb is consistent with the standard model predictions. The following limits on ZZZ and ZZ-gamma anomalous trilinear gauge couplings are set at 95% confidence level: -0.011 < f(4)(Z) < 0.012, -0.012 < f(5)(Z) < 0.012, -0.013 < f(4)(gamma) < 0.015, and -0.014 < f(5)(gamma) < 0.014.Article Citation - WoS: 58Citation - Scopus: 58Search for Narrow Resonances and Quantum Black Holes in Inclusive and B-Tagged Dijet Mass Spectra From Pp Collisions at Root S=7 Tev(Springer Verlag, 2013) Karapınar, Güler; Demir, Durmuş AliA search for narrow resonances and quantum black holes is performed in inclusive and b-tagged dijet mass spectra measured with the CMS detector at the LHC. The data set corresponds to 5 fb(-1) of integrated luminosity collected in pp collisions at root s = 7 TeV. No narrow resonances or quantum black holes are observed. Model-independent upper limits at the 95% confidence level are obtained on the product of the cross section, branching fraction into dijets, and acceptance for three scenarios: decay into quark-quark, quark-gluon, and gluon-gluon pairs. Specific lower limits are set on the mass of string resonances (4.31 TeV), excited quarks (3.32 TeV), axigluons and colorons (3.36 TeV), scalar color-octet resonances (2.07 TeV), E-6 diquarks (3.75 TeV), and on the masses of W' (1.92 TeV) and Z' (1.47 TeV) bosons. The limits on the minimum mass of quantum black holes range from 4 to 5.3 TeV. In addition, b-quark tagging is applied to the two leading jets and upper limits are set on the production of narrow dijet resonances in a model-independent fashion as a function of the branching fraction to b-jet pairs.Article Citation - WoS: 180Citation - Scopus: 112Search for Neutral Mssm Higgs Bosons Decaying To a Pair of Tau Leptons in Pp Collisions(Springer Verlag, 2014) Karapınar, Güler; Demir, Durmuş AliA search for neutral Higgs bosons in the minimal supersymmetric extension of the standard model (MSSM) decaying to tau-lepton pairs in pp collisions is performed, using events recorded by the CMS experiment at the LHC. The dataset corresponds to an integrated luminosity of 24.6 fb(-1), with 4.9 fb(-1) at 7TeV and 19.7 fb(-1) at 8TeV. To enhance the sensitivity to neutral MSSM Higgs bosons, the search includes the case where the Higgs boson is produced in association with a b-quark jet. No excess is observed in the tau-lepton-pair invariant mass spectrum. Exclusion limits are presented in the MSSM parameter space for different benchmark scenarios, m(h)(max), m(h)(mod+), m(h)(mod-), light-stop, light-stau, T-phobic, and low-m(H). Upper limits on the cross section times branching fraction for gluon fusion and b-quark associated Higgs boson production are also given.