Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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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 AmericaArticle Citation - WoS: 28Search for a Heavy Bottom-Like Quark in Pp Collisions at Root S=7 Tev(Elsevier Ltd., 2011) Demir, Durmuş Ali; Karapınar, GülerA search for pair-produced bottom-like quarks in pp collisions at root s = 7 TeV is conducted with the CMS experiment at the LHC. The decay b' -> tW is considered in this search. The b'(b) over bar' tW-(t) over barW(+) process can be identified by the distinctive signature of trileptons and same-sign dileptons. With a data sample corresponding to an integrated luminosity of 34 pb(-1), no excess above the standard model background predictions is observed and a b' quark with a mass between 255 and 361 GeV/c(2) is excluded at the 95% confidence level. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.Article Citation - WoS: 21Measurement of the Ratio of the 3-Jet To 2-Jet Cross Sections in Pp Collisions at Root S=7 Tev(Elsevier Ltd., 2011) Demir, Durmuş Ali; Karapınar, GülerA measurement of the ratio of the inclusive 3-jet to 2-jet cross sections as a function of the total jet transverse momentum. HT, in the range 0.2 < H-T < 2.5 TeV is presented. The data have been collected at a proton-proton centre-of-mass energy of 7 TeV with the CMS detector at the LHC, and correspond to an integrated luminosity of 36 pb(-1). Comparisons are made between the data and the predictions of different QCD-based Monte Carlo models for multijet production. All models considered in this study are consistent with the data for H-T > 0.5 TeV. This measurement extends to an H-T range that has not been explored before. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.Article Citation - WoS: 33Search for Physics Beyond the Standard Model Using Multilepton Signatures in Pp Collisions at Root S=7 Tev(Elsevier Ltd., 2011) Demir, Durmuş Ali; Karapınar, GülerA search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to 35 pb(-1) of integrated luminosity in pp collisions at root s = 7 TeV collected by the CMS experiment at the LHC. A number of exclusive multileptonic channels are investigated and standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimise the reliance on simulation. The observations are consistent with background expectations. These results constrain previously unexplored regions of supersymmetric parameter space. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.Article Citation - WoS: 100Citation - Scopus: 81Search for Physics Beyond the Standard Model in Final States With a Lepton and Missing Transverse Energy in Proton-Proton Collisions at Root S = 8 Tev(American Physical Society, 2015) Demir, Durmuş Ali; Karapınar, GülerA search for new physics in proton-proton collisions having final states with an electron or muon and missing transverse energy is presented. The analysis uses data collected in 2012 with the CMS detector, at an LHC center-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of 19.7 fb(-1). No significant deviation of the transverse mass distribution of the charged lepton-neutrino system from the standard model prediction is found. Mass exclusion limits of up to 3.28 TeVat 95% confidence level for a W0-boson with the same couplings as that of the standard model W-boson are determined. Results are also derived in the framework of split universal extra dimensions, and exclusion limits on Kaluza-Klein Wd(KK)((2)) states are found. The final state with large missing transverse energy also enables a search for dark matter production with a recoiling W-boson, with limits set on the mass and the production cross section of potential candidates. Finally, limits are established for a model including interference between a left-handed W'-boson and the standard model W-boson and for a compositeness model.Conference Object Can Cpt Be Violated Through Extended Time Reversal?(World Scientific Publishing, 2001) Erdem, Recai; Ufuktepe, ÜnalWe consider the implications of the extension of time reversal through Wigner types and group extensions. We clarify its physical content and apply the results in a toy model. Finally we point out the possibility of violation of CPT in this framework.Conference Object Probing the Density of States of High Temperature Superconductors With Point Contact Tunneling Spectroscopy(Springer Verlag, 2005) Özyüzer, Lütfi; Zasadzinski, John F.; Miyakawa, Nobuaki; Gray, Kenneth E.Tunneling spectroscopy measurements are performed on single crystals of single CuO2 layer Tl2Ba2CuO6+delta, double CuO2 layer Bi2Sr2CaCu2O8+delta (Bi2212) and polycrystal quadruple CuO2 layer CuBa2Ca3Cu4O12+delta using the point contact tunneling technique. I-V and dI/dV-V characteristics are obtained at 4.2 K. In spite of different number of layers and T-c values, all three high-T-c superconductors exhibit similar spectral features including dip and hump features reminiscent of strong-coupling effects in conventional superconductors. The doping dependence of Bi2212 is studied and several effects of the hole concentration on spectral features are found. A novel effect is that the energy gap increases in the underdoped region even as T-c decreases. Combining the doping dependence of the energy gap and the dip energy provides additional information in order to understand the mechanism of high-T-c superconductivity. Point contact tunneling studies of the doping dependence of the energy gap in Bi2212 also helped to understand local variations of the gap magnitude observed by scanning tunneling microscopy, indicating that this type of spectroscopy is an integral part of the tunneling technique.Conference Object Citation - WoS: 7Citation - Scopus: 7Carbon Deposition on the Stainless Steels Substrates Using Pulsed Plasma(National Institute of Optoelectronics, 2008) Pat, Suat; Balbağ, Zafer; Cenik, I.; Ekem, Naci; Okur, Salih; Vladoiu, Rodica; Musa, GeavitWe have developed a generic method for carbon deposition method for any substrates from methane pulsed plasma. The generic method has been developed for carbon deposition on the stainless steels substrates using pulsed methane plasma. Pulsed plasma was produced at atmospheric pressure methane gas and room temperatures. Methane plasma was generated using with 25kV, 25kHz pulsed power supply. Discharge current approximately 300 mA. Stainless steels probes hold in the 32mm from the methane plasma. Probes dimensions were phi=30mm, h=8mm and 4 mm.