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Publication Open Access Early/fast VLF events produced by the quiescent heating of the lower ionosphere by thunderstorms(American Geophysical Union (AGU), 2017) Kabirzadeh, R.; Marshall, R. A.; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; İnan, Umran Savaş; Faculty Member; College of Engineering; 177880Large and easily distinguishable perturbations of the VLF transmitter signals due to interactions with thundercloud-driven ionospheric modifications have been observed and studied for about three decades. These events are called "early/fast VLF" or "early VLF" events due to their immediate detection (similar to 20 ms) after the causative lightning flash on the ground and the fast rise time of the perturbed signal. Despite many years of study, the physical mechanisms responsible for these perturbations are still under investigation. Modifications of the sustained heating level of the ionosphere due to a lightning flash has been previously proposed as the causative mechanism of early/fast VLF events. The perturbations predicted by this mechanism, however, have been much smaller than experimental observations of 0.2-1 dB or higher. In this study, by using an improved 3-D thundercloud electrostatic upward coupling model which uses a realistic geomagnetic field, we find that the sustained heating model can predict perturbations that are consistent with reported experimental observations. Modifications in the quiescent heating of the lower ionosphere by thundercloud fields by individual lightning flashes may thus account for some observations of early/fast VLF events. Large and easily distinguishable perturbations of the VLF transmitter signals due to interactions with thundercloud-driven ionospheric modifications have been observed and studied for about three decades. These events are called "early/fast VLF" or "early VLF" events due to their immediate detection (similar to 20 ms) after the causative lightning flash on the ground and the fast rise time of the perturbed signal. Despite many years of study, the physical mechanisms responsible for these perturbations are still under investigation. Modifications of the sustained heating level of the ionosphere due to a lightning flash has been previously proposed as the causative mechanism of early/fast VLF events. The perturbations predicted by this mechanism, however, have been much smaller than experimental observations of 0.2-1 dB or higher. In this study, by using an improved 3-D thundercloud electrostatic upward coupling model which uses a realistic geomagnetic field, we find that the sustained heating model can predict perturbations that are consistent with reported experimental observations. Modifications in the quiescent heating of the lower ionosphere by thundercloud fields by individual lightning flashes may thus account for some observations of early/fast VLF events.Publication Open Access A stochastic representation for mean curvature type geometric flows(Institute of Mathematical Statistics (IMS), 2003) Touzi, N.; Department of Mathematics; Department of Mathematics; Soner, Halil Mete; Faculty Member; College of Administrative Sciences and EconomicsA smooth solution {Gamma(t)}(tis an element of[0,T]) subset of R-d of a parabolic geometric flow is characterized as the reachability set of a stochastic target problem. In this control problem the controller tries to steer the state process into a given deterministic set T with probability one. The reachability set, V(t), for the target problem is the set of all initial data x from which the state process X-X(v)(t) is an element of T for some control process v. This representation is proved by studying the squared distance function to Gamma(t). For the codimension k mean curvature flow, the state process is dX(t) = root2P dW(t), where W(t) is a d-dimensional Brownian motion, and the control P is any projection matrix onto a (d - k)-dimensional plane. Smooth solutions of the inverse mean curvature flow and a discussion of non smooth solutions are also given.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; Department of Electrical and Electronics Engineering; Department of Physics; Çankaya, Hüseyin; Görgülü, Adil Tolga; Sennaroğlu, Alphan; Researcher; Master Student; Faculty Member; 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 Pneumonia in HIV-infected patients(Aves, 2016) Önür, Seda Tural; Dalar, Levent; Yalçın, Arzu Didem; İliaz, Sinem; Doctor; Koç University Hospital; 168584Acquired immune deficiency syndrome (AIDS) is an immune system disease caused by the human immunodeficiency virus (HIV). The purpose of this review is to investigate the correlation between an immune system destroyed by HIV and the frequency of pneumonia. Observational studies show that respiratory diseases are among the most common infections observed in HIV-infected patients. In addition, pneumonia is the leading cause of morbidity and mortality in HIV-infected patients. According to articles in literature, in addition to antiretroviral therapy (ART) or highly active antiretroviral therapy (HAART), the use of prophylaxis provides favorable results for the treatment of pneumonia. Here we conduct a systematic literature review to determine the pathogenesis and causative agents of bacterial pneumonia, tuberculosis (TB), nontuberculous mycobacterial disease, fungal pneumonia, Pneumocystis pneumonia, viral pneumonia and parasitic infections and the prophylaxis in addition to ART and HAART for treatment. Pneumococcus-based polysaccharide vaccine is recommended to avoid some type of specific bacterial pneumonia.Publication Open Access Multidimensional wave packet dynamics within the fluid dynamical formulation of the Schrodinger equation(American Institute of Physics (AIP) Publishing, 1998) Rabitz, H.; Department of Mathematics; Department of Mathematics; Aşkar, Attila; Dey, Bijoy K.; Faculty Member; Faculty Member; College of Sciences; 178822; N/AThis paper explores the quantum fluid dynamical (QFD) representation of the time-dependent Schrodinger equation for the motion of a wave packet in a high dimensional space. A novel alternating direction technique is utilized to single our each of the many dimensions in the QFD equations. This technique is used to solve the continuity equation for the density and the equation for the convection of the flux for the quantum particle. The ability of the present scheme to efficiently and accurately describe the dynamics of a quantum particle is demonstrated in four dimensions where analytical results are known. We also apply the technique to the photodissociation of NOCl and NO2 where the systems are reduced to two coordinates by freezing the angular variable at its equilibrium value.Publication Open Access TRMU-related transient liver failure of infancy presents with microcephaly and neurodevelopmental delay(Nature Publishing Group (NPG), 2019) N/A; N/A; Azaklı, Hülya; Börklü Yücel, Esra; Arıkan, Çiğdem; Armutlu, Ayşe; Eraslan, Serpil; Kayserili, Hülya; PhD Student; Faculty Member; Teaching Faculty; Researcher; Graduate School of Health Sciences; School of Medicine; N/A; N/A; N/A; N/A; N/A; 7945Publication Open Access How do mega-bank merger policy and regulations contribute to financial stability? Evidence from Australia and Canada(Taylor _ Francis, 2017) Department of International Relations; Department of International Relations; Bakır, Caner; Faculty Member; College of Administrative Sciences and Economics; 108141Although the role of financial regulatory failures in the global financial crisis (GFC) has been explored extensively in the post-GFC literature, our knowledge of the role of bank merger and takeover policy and regulation in reinforcing financial stability is limited. Based on an exploratory case study of Australia, which is examined in comparison to Canada, this article argues that competition policy and regulation contributed to financial stability by insulating the largest Australian and Canadian banks from domestic or foreign hostile takeover threats, and by limiting their asset size, and thus their internationalization and interconnections with the global banking community.Publication Open Access HF beam parameters in ELF/VLF wave generation via modulated heating of the ionosphere(American Geophysical Union (AGU), 2012) Cohen, M. B.; Golkowski, M.; Lehtinen, N. G.; McCarrick, M. J.; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; İnan, Umran Savaş; Faculty Member; College of Engineering; 177880ELF/VLF (0.3–30 kHz) wave generation is achievable via modulated HF (3–30 MHz) heating of the lower ionosphere in the presence of natural currents such as the auroral electrojet. Using the 3.6 MW High Frequency Active Auroral Research Program (HAARP) facility near Gakona, AK, we investigate the effect of HF frequency and beam size on the generated ELF/VLF amplitudes, as a function of modulation frequency, and find that generation in the Earth-ionosphere waveguide generally decreases with increasing HF frequency between 2.75–9.50 MHz. HAARP is also capable of spreading the HF power over a wider area, and we find that a larger beam area yields larger generated amplitudes on the ground. Measurements are shown to generally agree with a theoretical model, which is then applied to also predict the effect of HF beam parameters on magnetospheric injection with HAARP.Publication Open Access Effectiveness of posterior structures in the development of proximal junctional kyphosis following posterior instrumentation: a biomechanical study in a sheep spine model(Elsevier, 2019) Akgül, Turgut; Sarıyılmaz, Kerim; Özkunt, Okan; Dikici, Fatih; Yazıcıoğlu, Önder; N/A; Korkmaz, Murat; Doctor; School of MedicineIntroduction: proximal junctional kyphosis – PJK has been defined by a 10 or greater increase in kyphosis at the proximal junction as measured by the Cobb angle from the caudal endplate of the uppermost instrumented vertebrae (UIV) to the cephalad endplate of the vertebrae 1 segments cranial to the UIV. In this biomechanical study, it is aimed to evaluate effects of interspinosus ligament complex distruption and facet joint degeneration on PJK development. Materials and methods: posterior instrumentation applied between T2 – T7 vertebrae using pedicle screws to randomly selected 21 sheeps, divided into 3 groups. First group selected as control group (CG), of which posterior soft tissue and facet joints are protected. In second group (spinosus group, SG) interspinosus ligament complex which 1 segment cranial to UIV has been transected, and third group (faset group-FG) was applied facet joint excision. 25 N, 50 N, 100 N, 150 N and 200 N forces applied at frequency of 5 Hertz as 100 cycles axial to the samples. Then, 250 N, 275 N and 300 N forces applied static axially. Interspinosus distance, kyphosis angle and discus heights was measured in radiological evaluation. Abnormal PJK was defined by a proximal junctional angle greater than 100 and at least 100 greater than the corresponding preoperative measurement. Results: in CG group, average interspinosus distance was 6,6 ± 1.54 mm and kyphosis angle was 2,2 ± 0.46° before biomechanical testing, and they were measured as 9,4 ± 1.21 mm and 3,3 ±0.44° respectively after forces applied to samples. In SG group, average interspinosus distance was 6,2 ± 1.72 mm and kyphosis angle was 2,7 ± 1.01° before experiment, and they were measured as 20,8 ± 5.66 mm and 15,1 ± 2.34° respectively after forces applied to samples. In FG group, average interspinosus distance was 4,8 ± 1.15 mm and kyphosis angle was −1 ± 4.14° before experiment, and they were measured as 11,1 ±1.96mm and 11 ± 2.87° respectively after forces applied to samples. In comparison to group CG, statistically significant junctional kyphosis was seen on both FG and SG group after statistical analysis. (p < 0.05). PJK was seen statistically significant more on SG group than FG group. (p < 0.05). Not any statistically significant difference was seen on measurement of disk distances among three groups. (p > 0.05) Conclusions: protecting interspinosus ligament complex and facet joint unity during posterior surgical treatment for spine deformation is vital to prevent PJK development. Based on our literature review, this is the first biomechanical study that reveals interspinosus ligament complex are more effective on preventing PJK development than facet joints.Publication Open Access Observation of two-photon interference using the zero-phonon-line emission of a single molecule(Institute of Physics (IOP) Publishing, 2006) Ehrl, M.; Hellerer, Th.; Brauchle, C.; Zumbusch, A.; Department of Physics; Department of Physics; Müstecaplıoğlu, Özgür Esat; Kiraz, Alper; Faculty Member; Faculty Member; College of Sciences; 1674; 22542We report the results of coincidence counting experiments at the output of a Michelson interferometer using the zero-phonon-line emission of a single molecule at 1.4 K. Under continuous wave excitation, we observe the absence of coincidence counts as an indication of two-photon interference. This corresponds to the observation of Hong-Ou-Mandel correlations.