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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Comparative spectroscopic investigation of Tm3+: tellurite glasses for 2-mu m lasing applications(Multidisciplinary Digital Publishing Institute (MDPI), 2018) Kurt, Adnan; Speghini, Adolfo; Bettinelli, Marco; Department of Electrical and Electronics Engineering; Department of Physics; Çankaya, Hüseyin; Görgülü, Adil Tolga; Sennaroğlu, Alphan; Researcher; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; College of Sciences; N/A; N/A; 23851We performed a comparative spectroscopic analysis on three novel Tm3+: tellurite-based glasses with the following compositions Tm2O3: TeO2-ZnO (TeZnTm), Tm2O3: TeO2-Nb2O5 (TeNbTm), and Tm3+: TeO2-K2O-Nb2O5 (TeNbKTm), primarily for 2-mu m laser applications. Tellurite glasses were prepared at different doping concentrations in order to investigate the effect of Tm3+ ion concentration as well as host composition on the stimulated emission cross sections and the luminescence quantum efficiencies. By performing Judd-Ofelt analysis, we determined the average radiative lifetimes of the H-3(4) level to be 2.55 +/- 0.07 ms, 2.76 +/- 0.03 ms and 2.57 +/- 0.20 ms for the TeZnTm, TeNbTm and TeNbKTm samples, respectively. We clearly observed the effect of the cross-relaxation, which becomes significant at higher Tm2O3 concentrations, leading to the quenching of 1460-nm emission and enhancement of 1860-nm emission. Furthermore, with increasing Tm2O3 concentrations, we observed a decrease in the fluorescence lifetimes as a result of the onset of non-radiative decay. For the H-3(4) level, the highest obtained quantum efficiency was 32% for the samples with the lowest Tm2O3 ion concentration. For the 1860-nm emission band, the average emission cross section was determined to measure around 6.33 +/- 0.34 x 10(-21) cm(2), revealing the potential of thulium-doped tellurite gain media for 2-mu m laser applications in bulk and fiber configurations.Publication Open Access A note on the pp-wave solution of minimal massive 3D gravity coupled with Maxwell-Chern-Simons theory(Institute of Physics (IOP) Publishing, 2022) Cebeci, Hakan; Şentorun, Seçil; Department of Physics; Dereli, Tekin; Faculty Member; Department of Physics; College of Sciences; 201358In this work, we examine a family of pp-wave solutions of minimal massive 3D gravity minimally coupled with the Maxwell-Chern-Simons theory. An elaborate investigation of the field equations shows that the theory admits pp-wave solutions provided that there exist an anti-self duality relation between the electric and the magnetic components of the Maxwell two-form field. By employing Noether-Wald formalism, we also construct Noether charges of the theory within exterior algebra formalism.Publication Open Access Chaotic spin correlations in frustrated Ising hierarchical lattices(American Physical Society (APS), 2009) Berker, A. Nihat; Department of Physics; Aral, Neşe; Department of Physics; College of SciencesSpin-spin correlations are calculated in frustrated hierarchical Ising models that exhibit chaotic renormalization-group behavior. The spin-spin correlations, as a function of distance, behave chaotically. The far correlations, but not the near correlations, are sensitive to small changes in temperature or frustration, with temperature changes having a larger effect. On the other hand, the calculated free energy, internal energy, and entropy are smooth functions of temperature. The recursion-matrix calculation of thermodynamic densities in a chaotic band is demonstrated. The leading Lyapunov exponents are calculated as a function of frustration.Publication Open Access Field-driven hysteresis of the d=3 Ising spin glass: hard-spin mean-field theory(American Physical Society (APS), 2007) Yücesoy, Burcu; Department of Physics; Berker, Ahmet Nihat; Faculty Member; Department of Physics; College of SciencesHysteresis loops are obtained in the Ising spin-glass phase in d=3 using frustration-conserving hard-spin mean-field theory. The system is driven by a time-dependent random magnetic field H-Q that is conjugate to the spin-glass order Q, yielding a field-driven first-order phase transition through the spin-glass phase. The hysteresis loop area A of the Q-H-Q curve scales with respect to the sweep rate h of magnetic field as A-A(0)similar to h(b). In the spin-glass and random-bond ferromagnetic phases, the sweep-rate scaling exponent b changes with temperature T but appears not to change with antiferromagnetic bond concentration p. By contrast, in the pure ferromagnetic phase, b does not depend on T and has a sharply different value than in the two other phases.Publication Open Access Understanding the link between inflammasome and apoptosis through the response of THP-1 cells against drugs using droplet-based microfluidics(American Chemical Society (ACS), 2022) Gençtürk, E.; Kasım, M.; Ülgen, K.O.; Department of Physics; Department of Electrical and Electronics Engineering; Kiraz, Alper; Morova, Berna; Faculty Member; Researcher; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; College of Engineering; 22542; N/ADroplet-based microfluidic devices are used to investigate monocytic THP-1 cells in response to drug administration.Consistent and reproducible droplets are created, each of which acts as a bioreactor to carry out single cell experiments withminimized contamination and live cell tracking under an invertedfluorescence microscope for more than 2 days. Here, the effects ofthree different drugs (temsirolimus, rifabutin, and BAY 11-7082) on THP-1 are examined and the results are analyzed in the contextof the inflammasome and apoptosis relationship. The ASC adaptor gene tagged with GFP is monitored as the inflammasomereporter. Thus, a systematic way is presented for deciphering cell-to-cell heterogeneity, which is an important issue in cancertreatment. The drug temsirolimus, which has effects of disrupting the mTOR pathway and triggering apoptosis in tumor cells, causesTHP-1 cells to express ASC and to be involved in apoptosis. Treatment with rifabutin, which inhibits proliferation and initiatesapoptosis in cells, affects ASC expression byfirst increasing and then decreasing it. CASP-3, which has a role in apoptosis and isdirectly related to ASC, has an increasing level in inflammasome conditioning. Thus, the cell under the effect of rifabutin might befaced with programmed cell death faster. The drug BAY 11-7082, which is responsible for NF Kappa B inhibition, shows similar results totemsirolimus with more than 60% of cells having highfluorescence intensity (ASC expression). The microfluidic platform presentedhere offers strong potential for studying newly developed small-molecule inhibitors for personalized/precision medicine.Publication Open Access Phase separation and charge-ordered phases of the d=3 Falicov-Kimball model at nonzero temperature: temperature-density-chemical potential global phase diagram from renormalization-group theory(American Physical Society (APS), 2011) Hinczewski, Michael; Department of Physics; Sarıyer, Ozan; Berker, Ahmet Nihat; Faculty Member; Department of Physics; College of SciencesThe global phase diagram of the spinless Falicov-Kimball model in d = 3 spatial dimensions is obtained by renormalization-group theory. This global phase diagram exhibits five distinct phases. Four of these phases are charge-ordered (CO) phases, in which the system forms two sublattices with different electron densities. The CO phases occur at and near half filling of the conduction electrons for the entire range of localized electron densities. The phase boundaries are second order, except for the intermediate and large interaction regimes, where a first-order phase boundary occurs in the central region of the phase diagram, resulting in phase coexistence at and near half filling of both localized and conduction electrons. These two-phase or three-phase coexistence regions are between different charge-ordered phases, between charge-ordered and disordered phases, and between dense and dilute disordered phases. The second-order phase boundaries terminate on the first-order phase transitions via critical endpoints and double critical endpoints. The first-order phase boundary is delimited by critical points. The cross-sections of the global phase diagram with respect to the chemical potentials and densities of the localized and conduction electrons, at all representative interactions strengths, hopping strengths, and temperatures, are calculated and exhibit ten distinct topologies.Publication Open Access Few-qubit quantum refrigerator for cooling a multi-qubit system(Nature Publishing Group (NPG), 2021) Arısoy, Onat; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We propose to use a few-qubit system as a compact quantum refrigerator for cooling an interacting multi-qubit system. We specifically consider a central qubit coupled to N ancilla qubits in a so-called spin-star model to be used as refrigerant by means of short interactions with a many-qubit system to be cooled. We first show that if the interaction between the qubits is of the longitudinal and ferromagnetic Ising model form, the central qubit is colder than the environment. We summarize how preparing the refrigerant qubits using the spin-star model paves the way for the cooling of a many-qubit system by means of a collisional route to thermalization. We discuss a simple refrigeration cycle, considering the operation cost and cooling efficiency, which can be controlled by N and the qubit–qubit interaction strength. Besides, bounds on the achievable temperature are established. Such few-qubit compact quantum refrigerators can be significant to reduce dimensions of quantum technology applications, can be easy to integrate into all-qubit systems, and can increase the speed and power of quantum computing and thermal devices.Publication Open Access Laser-inscribed diamond waveguide resonantly coupled to diamond microsphere(Multidisciplinary Digital Publishing Institute (MDPI), 2020) Le Phu, T.; Giakoumaki, A.; Bharadwaj, V.; Ramponi, R.; Eaton, S.M.; Department of Physics; Yavuz, Nurperi; Bayer, Mustafa Mert; Çirkinoğlu, Hüseyin Ozan; Serpengüzel, Ali; Master Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 27855An all-diamond photonic circuit was implemented by integrating a diamond microsphere with a femtosecond-laser-written bulk diamond waveguide. The near surface waveguide was fabricated by exploiting the Type II fabrication method to achieve stress-induced waveguiding. Transverse electrically and transverse magnetically polarized light from a tunable laser operating in the near-infrared region was injected into the diamond waveguide, which when coupled to the diamond microsphere showed whispering-gallery modes with a spacing of 0.33 nm and high-quality factors of 105. By carefully engineering these high-quality factor resonances, and further exploiting the properties of existing nitrogen-vacancy centers in diamond microspheres and diamond waveguides in such configurations, it should be possible to realize filtering, sensing and nonlinear optical applications in integrated diamond photonics.Publication Open Access Frustrated further-neighbor antiferromagnetic and electron-hopping interactions in the d=3 t-J model: finite-temperature global phase diagrams from renormalization group theory(American Physical Society (APS), 2009) Hinczewski, Michael; Department of Physics; Kaplan, C. Nadir; Berker, Ahmet Nihat; Faculty Member; Department of Physics; College of SciencesThe renormalization-group theory of the d=3 t-J model is extended to further-neighbor antiferromagnetic or electron-hopping interactions, including the ranges of frustration. The global phase diagram of each model is calculated for the entire ranges of temperatures, electron densities, further/first-neighbor interaction-strength ratios. With the inclusion of further-neighbor interactions, an extremely rich phase diagram structure is found and is explained by competing and frustrated interactions. In addition to the tau(tJ) phase seen in earlier studies of the nearest-neighbor d=3 t-J model, the tau(Hb) phase seen before in the d=3 Hubbard model appears both near and away from half filling.Publication Open Access Gravitational plane waves in a non-Riemannian description of Brans-Dicke gravity(Institute of Physics (IOP) Publishing, 2020) Department of Physics; Dereli, Tekin; Şenikoğlu, Yorgo; Researcher; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; 201358; N/AThe gravitational field equations of Brans-Dicke theory are given in a 4-dimensional non-Riemannian space-time with torsion in the language of exterior differential forms A class of pp-wave metrics together with the Brans-Dicke scalar field are used to derive the autoparallel equations of motion for non-spinning test masses. These are compared with the geodesic equations of motion and the differences are pointed out. The effects of the gradient of the Brans-Dicke scalar on the geodesic deviation equations in this non-Riemannian setting are also discussed.