Browsing Scholarly Publications by Type "Article"
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Item Open Access1 mJ pulse bursts from a Yb-doped fiber amplifier(Optical Society of America, 2012-07-01) Kalaycıoğlu, Hamit; Eldeniz, Y. B.; Akçalan, Önder; Yavaş, Seydi; Efe, M.; İlday, Fatih Ömer; Kalaycıoğlu, Hamit; Akçalan, Önder; Yavaş, Seydi; İlday, Fatih ÖmerWe demonstrate burst-mode operation of a polarization-maintaining Yb-doped fiber amplifier capable of generating 60 μJ pulses within bursts of 11 pulses with extremely uniform energy distribution facilitated by a novel feedback mechanism shaping the seed of the burst-mode amplifier. The burst energy can be scaled up to 1 mJ, comprising 25 pulses with 40 μJ average individual energy. The amplifier is synchronously pulse pumped to minimize amplified spontaneous emission between the bursts. Pulse propagation is entirely in fiber and fiber-integrated components until the grating compressor, which allows for highly robust operation. The burst repetition rate is set to 1 kHz and spacing between individual pulses is 10 ns. The 40 μJ pulses are externally compressible to a full width at half-maximum of 600 fs. However, due to the substantial pedestal of the compressed pulses, the effective pulse duration is longer, estimated to be 1.2 ps. Item Open Access1.3 μm GaAs based resonant cavity enhanced Schottky barrier internal photoemission photodetector(IEEE, Piscataway, NJ, United States, 2000) Necmi, B.; Kimukin, I.; Özbay, Ekmel; Tuttle, G.; Özbay, EkmelGaAs based photodetectors operating at 1.3 μm that depend on internal photoemission as the absorption mechanism were fabricated. Quantum efficiency (QE) was increased using resonant cavity enhancement (RCE) effect. Item Restricted1.5D parallel sparse matrix-vector multiply(Society for Industrial and Applied Mathematics, 2018) Kayaaslan, E.; Aykanat, Cevdet; Uçar, B.; Aykanat, CevdetThere are three common parallel sparse matrix-vector multiply algorithms: 1D row-parallel, 1D column-parallel, and 2D row-column-parallel. The 1D parallel algorithms offer the advantage of having only one communication phase. On the other hand, the 2D parallel algorithm is more scalable, but it suffers from two communication phases. Here, we introduce a novel concept of heterogeneous messages where a heterogeneous message may contain both input-vector entries and partially computed output-vector entries. This concept not only leads to a decreased number of messages but also enables fusing the input- and output-communication phases into a single phase. These findings are exploited to propose a 1.5D parallel sparse matrix-vector multiply algorithm which is called local row-column-parallel. This proposed algorithm requires a constrained fine-grain partitioning in which each fine-grain task is assigned to the processor that contains either its input-vector entry, its output-vector entry, or both. We propose two methods to carry out the constrained fine-grain partitioning. We conduct our experiments on a large set of test matrices to evaluate the partitioning qualities and partitioning times of these proposed 1.5D methods. Item Open Access1/f Noise characteristics of SEJ Y-Ba-Cu-O Rf-SQUIDs on LaAlO3 substrate and the step structure, film, and temperature dependence(IEEE, 2001-03) Fardmanesh, M.; Schubert, J.; Akram, R.; Bick, M.; Zhang, Y.; Banzet, M.; Zander, W.; Krause, H. J.; Burkhart, H.; Schilling, M.Step edge junction (SEJ) rf-SQUID magnetometers and gradiometers were fabricated using PLD Y-Ea-Cu-0 films on LaA10,(100) and SrTi0,(100) substrates. Effects of different step structure and the film properties on the yield, optimal operating temperature, and the l/f noise of the SQUIDs were investigated. The step structure was controlled using various IBE processes. The devices on LaAIO, showed higher sensitivity to the step structure compared to those on SrTiO,. This was due to re-deposition of substrate material at the steps prepared using the conventional IBE process resulting in a very low yield of unstable SQUIDs. High yield of low l/f noise stable SQUIDs was obtained on LaAIO, substrates with sharp steps prepared using an optimized IBE process. A typical l/f noise corner frequency of about lOHz at 77K with two major temperature dependencies was obtained. The temperature dependencies of the l/f noise could be correlated to the junction and the film of washer area of the SQUIDS. The white noise of our devices showed a dependency mainly on the amplitude of the flux to voltage transfer function signal. The operating temperature range of the SQUIDs could be controlled by the step structure and narrowed when the optimal operating temperature range was increased. All the measured junctions of our devices on the modified steps showed RSJ type behavior with a moderate decrease of the R, versus temperature. Item Open Access10 yıl sonra Dede Korkut Oğuznameleri ve notlar(Geleneksel Yayıncılık, 2010) Özay, Y.Semih Tezcan ve Hendrik Boeschoten’in hazırladıkları, 2001 yılında Yapı Kredi Yayınları’ndan çıkan Dede Korkut Oğuznameleri (316 s.) ile yine aynı yıl, aynı yayınevinden çıkan Semih Tezcan’ın hazırladığı Dede Korkut Oğuznameleri Üzerine Notlar (424 s.) adlı kitaplar üzerine yirmi üç kitap tanıtım ya da kitap eleştiri yazısı çıkmıştır. Türkiye’de yayınlanmış bir çalışma üzerine altısı uluslararası dergilerde olmak üzere bu kadar çok yazı yayınlanması öncelikle çalışmanın önemini ve ciddiyetini gösterir, bunun yanında bu yeni çalışma birçok araştırmacının dikkatini çekecek ve üzerinde yorum yapmasına teşvik edecek yeni bazı kapılar açmış olmalıdır. Bu yazıda, bu yeniliklerin neler olduğu, dokuz yıl içerisinde bu çalışmaların nasıl tepkiler aldığı, ilk kez bu çalışmalarda önerilen çözümlerin hangilerinin sorgulanmadan onaylandığı ve hangi çözümlerin eleştirildiği tartışmaya açılacaktır. Item Open Access100-GHz resonant cavity enhanced Schottky photodiodes(Institute of Electrical and Electronics Engineers, 1998) Onat, B. M.; Gökkavas, M.; Özbay, Ekmel; Ata, E. P.; Towe, E.; Ünlü, M. S.; Özbay, EkmelResonant cavity enhanced (RCE) photodiodes are promising candidates for applications in optical communications and interconnects where ultrafast high-efficiency detection is desirable. We have designed and fabricated RCE Schottky photodiodes in the (Al, In) GaAs material system for 900-nm wavelength. The observed temporal response with 10-ps pulsewidth was limited by the measurement setup and a conservative estimation of the bandwidth corresponds to more than 100 GHz. A direct comparison of RCE versus conventional detector performance was performed by high speed measurements under optical excitation at resonant wavelength (895 nm) and at 840 nm where the device functions as a single-pass conventional photodiode. A more than two-fold bandwidth enhancement with the RCE detection scheme was demonstrated. Item Open Access1018 nm Yb-doped high-power fiber laser pumped by broadband pump sources around 915 nm with output power above 100 W(OSA - The Optical Society, 2017) Midilli, Y.; Efunbajo, O. B.; Şimşek, B.; Ortaç, B.We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating in the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 to 924 nm by altering the cooling temperature of the pump diodes. Across this so-called pump wavelength regime having a 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB, showing good suppression ratio. Comparisons to the conventional 976 nm-pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experimentation and obtained 67% maximum optical-to-optical efficiency at an approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm reported in detail. Item Open Access15-Lipoxygenase-1 re-expression in colorectal cancer alters endothelial cell features through enhanced expression of TSP-1 and ICAM-1(Elsevier, 2017-11) Tunçer, S.; Keşküş, A. G.; Çolakoğlu, M.; Çimen, I.; Yener, C.; Konu, Ö.; Banerjee, S.15-lipoxygenase-1 (15-LOX-1) oxygenates linoleic acid to 13(S)-hydroxyoctadecadienoic acid (HODE). The enzyme is widely suppressed in different cancers and its re-expression has tumor suppressive effects. 15-LOX-1 has been shown to inhibit neoangiogenesis in colorectal cancer (CRC); in the present study we confirm this phenomenon and describe the mechanistic basis. We show that re-expression of 15-LOX-1 in CRC cell lines resulted in decreased transcriptional activity of HIF1α and reduced the expression and secretion of VEGF in both normoxic and hypoxic conditions. Conditioned medium (CM) was obtained from CRC or prostate cancer cell lines re-expressing 15-LOX-1 (15-LOX-1CM). 15-LOX-1CM treated aortic rings from 6-week old C57BL/6 mice showed significantly less vessel sprouting and more organized structure of vascular network. Human umbilical vein endothelial cells (HUVECs) incubated with 15-LOX-1CM showed reduced motility, enhanced expression of intercellular cell adhesion molecule (ICAM-1) and reduced tube formation but no change in proliferation or cell-cycle distribution. HUVECs incubated with 13(S)-HODE partially phenocopied the effects of 15-LOX-1CM, i.e., showed reduced motility and enhanced expression of ICAM-1, but did not reduce tube formation, implying the importance of additional factors. Therefore, a Proteome Profiler Angiogenesis Array was carried out, which showed that Thrombospondin-1 (TSP-1), a matrix glycoprotein known to strongly inhibit neovascularization, was expressed significantly more in HUVECs incubated with 15-LOX-1CM. TSP-1 blockage in HUVECs reduced the expression of ICAM-1 and enhanced cell motility, thereby providing a mechanism for reduced angiogenesis. The anti-angiogenic effects of 15-LOX-1 through enhanced expressions of ICAM-1 and TSP-1 are novel findings and should be explored further to develop therapeutic options. Item Open AccessThe 16 cubes game for children who are visually impaired(Sage Publications, Inc., 2000) Evyapan, N. A. G. Z.; Demirkan, H. Item Open Access1680-1747 Ottoman budgets and deficits sustainability in a period of fiscal transition: wars and administrative changes(American Economic Association, 2006) Berument, Hakan; Ocaklı, N.; Berument, HakanThis paper studies the sustainability of the Ottoman budget for the period from 1680 to 1747, during different sultanates and war eras. Moreover, we investigate whether the relationship between government revenues and expenditures changes in the period of culus. The empirical evidence gathered in this paper suggests that during the sample period, except for the sultanate era of Mahmut I, the Ottoman budget was not sustainable. The other interesting result of the study is that culus payments had a significant tax increasing effect. Moreover, the distribution of culus deteriorated the sustainability of budget. Item Open Access175 fs-long pulses from a high-power single-mode er-doped fiber laser at 1550 nm(Elsevier, 2017) Elahi, P.; Kalaycıoğlu, H.; Li, H.; Akçaalan, Ö.; Ilday, F. Ö.Development of Er-doped ultrafast lasers have lagged behind the corresponding developments in Yb- and Tm-doped lasers, in particular, fiber lasers. Various applications benefit from operation at a central wavelength of 1.5 μm and its second harmonic, including emerging applications such as 3D processing of silicon and 3D printing based on two-photon polymerization. We report a simple, robust fiber master oscillator power amplifier operating at 1.55 μm, implementing chirp pulse amplification using single-mode fibers for diffraction-limited beam quality. The laser generates 80 nJ pulses at a repetition rate of 43 MHz, corresponding to an average power of 3.5 W, which can be compressed down to 175 fs. The generation of short pulses was achieved using a design which is guided by numerical simulations of pulse propagation and amplification and manages to overturn gain narrowing with self-phase modulation, without invoking excessive Raman scattering processes. The seed source for the two-stage amplifier is a dispersion-managed passively mode-locked oscillator, which generates a ∼40 nm-wide spectrum and 1.7-ps linearly chirped pulses. Item Open Access18. yüzyılda klasik mesnevide değişim ve sürerlik bağlamında Şeyh Gâlib'in Hüsn ü Aşk'ının "Işıknâme" olarak kurgusu(Harvard University * Near Eastern Languages and Civilizations, 2013) Tezcan, N. Item Open Access1930 lu Yıllar Türkiye sinde Çanakkale savaşları nı anma etkinlikleri ve halkevlerinin rolü(Çanakkale Onsekiz Mart Üniversitesi, 2015) Ulaş, Tayfun; Ulaş, TayfunÇanakkale Savaşları, Türk halkı için mücadelenin ve zor bir dönemde yeniden varoluşun simgesidir. Çanakkale de kazanılan zafer evrensel mahiyettedir. Müteakiben Millî Mücadele dönemine de büyük etkisi söz konusudur. Bu çalışmada 1930 lu yıllarda, Çanakkale Savaşları nı anma etkinliklerinin nasıl bir süreç içerisinde geliştiği ve yurt genelinde halkın bu etkinliklere katılımının bilhassa Halkevleri kanadı ile ne şekilde olduğu üzerinde durulcaktır. Gerek basında yer alan etkinlikler, gerekse dönemin diğer yayınları ele alınarak bahsi geçen yıllarda gerçekleştirilen Çanakkale Savaşları nı anma etkinlikleri irdelenmeye gayret edilecektir. Item Open Access1982 T.C. Anayasası'nın vergi ödevi ile ilgili 73. maddesinin değerlendirilmesi(Maliye Hesap Uzmanları Derneği, 2016-07) Mutluer, M. Kamil; Dayanç, N. Nilay; Mutluer, M. Kamil; Dayanç, N. NilayBir ülkenin gelişmişliği o ülkedeki vergilendirme sistemi ile doğru orantılıdır. Vergilendirmeninkamu harcamalarının önemli bir finansmanı olmasının ötesinde gelir dağılımındaki eşitsizliği gidermek gibi sosyal amaçları da vardır. Buna rağmen, son zamanlarda ortaya konan istatistiklerde göstermektedir ki olması gereken vergi sisteminden büyük ölçüde uzaklaşılmıştır. Bu uzaklaşmanın altında yatan sebeplerden vergi psikolojisine yer verilmemiş olması, kanunların çok sık değişmesi ve dolaysız vergilerin vergi sistemi içindeki payının gitgide azalması gibi hususlara bumakale kapsamında değinilecek olup gelir harcama ve servet vergileri de bir analiz yapılacaktır Item Open Access1990 lı Yıllardan 2000 lere süregiden eğitilme sürecinin benlik inşasında yol açtığı hasarlar(2014) Yavuz, Ayşe Duygu; Yavuz, Ayşe Duygu Item Open Access2 + 1 KdV(N) equations(American Institute of Physics, 2011) Gürses, M.; Pekcan, A.We present some nonlinear partial differential equations in 2 + 1-dimensions derived from the KdV equation and its symmetries. We show that all these equations have the same 3-soliton solution structures. The only difference in these solutions are the dispersion relations. We also show that they possess the Painlevé property. © 2011 American Institute of Physics. Item Open Access(2 + 1)-dimensional AKNS(−N) systems II(Elsevier BV, 2021-06) Gürses, Metin; Pekcan, Aslı; Gürses, Metin; Pekcan, AslıIn our previous work (Gürses and Pekcan, 2019, ) we started to investigate negative AKNS(−N) hierarchy in (2 + 1)-dimensions. We were able to obtain only the first three, N = 0, 1, 2, members of this hierarchy. The main difficulty was the nonexistence of the Hirota formulation of the AKNS(N) hierarchy for N ≥ 3. Here in this work we overcome this difficulty for N = 3, 4 and obtain Hirota bilinear forms of (2 + 1)-dimensional AKNS(−N) equations for these members. We study the local and nonlocal reductions of these systems of equations and obtain several new integrable local and nonlocal equations in (2 + 1)- dimensions. We also give one-, two-, and three-soliton solutions of the reduced equations Item Open Access(2+1)-dimensional local and nonlocal reductions of the negative AKNS system: soliton solutions(Elsevier, 2018) Gürses, Metin; Pekcan, A.; Gürses, MetinWefirstconstructa(2+1)dimensionalnegativeAKNShierarchyandthenwegiveallpossiblelocaland(discrete)nonlocalreductionsoftheseequations.WefindHirotabilinearformsofthenegativeAKNShierarchyandgiveone-andtwo-solitonsolutions.ByusingthesolitonsolutionsofthenegativeAKNShierarchywefindone-solitonsolutionsofthelocalandnonlocalreducedequations. Item Open Access[2+2] cycloadditions of sorbyl tosylate with imines/1-azadienes: a one-pot domino approach for α-alkylidene-β-lactams and their computational studies and antimicrobial evaluation(Wiley-Blackwell, 2018) Kumar, Y.; Bedi, P. M. S.; Singh, P.; Adeniyi, A. A.; Singh-Pillay, A.; Singh, P.; Bhargava, G.The manuscript describes a straightforward and atom-efficient method for the synthesis of α-alkylidene-β-lactams using sorbyl tosylate and imines/1-azadienes at high temperature (80 °C). The Density functional theory calculations have shown the prevalence of the first order kinetics in these [2+2] cycloadditions to produce mixture of 3-butadienyl-azetidin-2ones and 3-but-2-enylidene-azetidin-2-ones in good yields. The 3-but-2-enylidene-azetidin-2-ones have also shown antimicrobial activity against the E. coli, S. aureus, P. aeruginosa, B. cereus and B. subtilis.