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Publication Metadata only ‘Anti-commutable’ local pre-Leibniz algebroids and admissible connections(Elsevier, 2023) Department of Physics; N/A; Dereli, Tekin; Doğan, Keremcan; Faculty Member; PhD Student; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; 201358; N/AThe concept of algebroid is convenient as a basis for constructions of geometrical frameworks. For example, metric-affine and generalized geometries can be written on Lie and Courant algebroids, respectively. Furthermore, string theories might make use of many other algebroids such as metric algebroids, higher Courant algebroids, or conformal Courant algebroids. Working on the possibly most general algebroid structure, which generalizes many of the algebroids used in the literature, is fruitful as it creates a chance to study all of them at once. Local pre-Leibniz algebroids are such general ones in which metric-connection geometries are possible to construct. On the other hand, the existence of the 'locality operator', which is present for the left-Leibniz rule for the bracket, necessitates the modification of torsion and curvature operators in order to achieve tensorial quantities. In this paper, this modification of torsion and curvature is explained from the point of view that the modification is applied to the bracket instead. This leads one to consider 'anti-commutable' local pre-Leibniz algebroids which satisfy an anti-commutativity-like property defined with respect to a choice of an equivalence class of connections. These 'admissible' connections are claimed to be the necessary ones while working on a geometry of algebroids. This claim is due to the fact that one can prove many desirable properties and relations if one uses only admissible connections. For instance, for admissible connections, we prove the first and second Bianchi identities, Cartan structure equations, Cartan magic formula, the construction of Levi-Civita connections, the decomposition of connection in terms of torsion and non-metricity. These all are possible because the modified bracket becomes anti-symmetric for an admissible connection so that one can apply the machinery of almost-or pre-Lie algebroids. We investigate various algebroid structures from the literature and show that they admit admissible connections which are metric-compatible in some generalized sense. Moreover, we prove that local pre-Leibniz algebroids that are not anti-commutable cannot be equipped with a torsion-free, and in particular Levi-Civita, connection.Publication Metadata only 10-NJ multipass-cavity femtosecond CR3+: LiCAF laser pumped by low-power single-mode diodes(Optical Society of America, 2009) Kärtner, Franz X.; Fujimoto, James G.; Demirbaş, Ümit; Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851We report on the generation of 9.9-nJ, 95-fs pulses at a repetition rate of 9.58 MHz from a multipass-cavity Cr3+:LiCAF laser pumped by single-mode diodes with a total absorbed pump power of only 540 mW.Publication Open Access 3D engineered neural co-culture model and neurovascular effects of marine fungi-derived citreohybridonol(American Institute of Physics (AIP) Publishing, 2022) Polat, İrem; Özkaya, Ferhat Can; El-Neketi, Mona; Ebrahim, Weaam; Şengül, Gülgün; Department of Mechanical Engineering; Sokullu, Emel; Sarabi, Misagh Rezapour; Taşoğlu, Savaş; Faculty Member; Faculty Member; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Koç Üniversitesi İş Bankası Yapay Zeka Uygulama ve Araştırma Merkezi (KUIS AI)/ Koç University İş Bank Artificial Intelligence Center (KUIS AI); KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); School of Medicine; Graduate School of Sciences and Engineering; College of Engineering; 163024; N/A; 291971Marine-based biomolecules are emerging metabolites that have gained attention for developing novel biomaterials, drugs, and pharmaceutical in vitro platforms. Here, we developed a 3D engineered neural co-culture model via a 3D prototyped sliding frame-platform for multi-step UV lithography and investigated the neurovascular potential of citreohybridonol in neuroblastoma treatment. Citreohybridonol was isolated from a sponge-derived fungus Penicillium atrovenetum. The model was characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy analysis. Human umbilical cord vein endothelial cells (HUVECs) and neuroblastoma (SH-SY5Y) cell lines were encapsulated in gelatin methacrylate (GelMA) with and without citreohybridonol. The effect of citreohybridonol on the proliferation capacity of cells was assessed via cell viability and immunostaining assays. GelMA and 3D culture characterization indicated that the cells were successfully encapsulated as axenic and mixed with/without citreohybridonol. The cytotoxic test confirmed that the 3D microenvironment was non-toxic for cultural experiments, and it showed the inhibitory effects of citreohybridonol on SH-SY5Y cells and induced the proliferation of HUVECs. Finally, immunohistochemical staining demonstrated that citreohybridonol suppressed SH-SY5Y cells and induced vascularization of HUVECs in mixed 3D cell culture.Publication Open Access 3D printing of elastomeric bioinspired complex adhesive microstructures(Wiley, 2021) Dayan, Cem Balda; Chun, Sungwoo; Krishna Subbaiah, Nagaraj; Drotlef, Dirk Michael; Akolpoğlu, Mükrime Birgül; Department of Mechanical Engineering; Sitti, Metin; Faculty Member; Department of Mechanical Engineering; College of Engineering; School of Medicine; 297104Bioinspired elastomeric structural adhesives can provide reversible and controllable adhesion on dry/wet and synthetic/biological surfaces for a broad range of commercial applications. Shape complexity and performance of the existing structural adhesives are limited by the used specific fabrication technique, such as molding. To overcome these limitations by proposing complex 3D microstructured adhesive designs, a 3D elastomeric microstructure fabrication approach is implemented using two-photon-polymerization-based 3D printing. A custom aliphatic urethane-acrylate-based elastomer is used as the 3D printing material. Two designs are demonstrated with two combined biological inspirations to show the advanced capabilities enabled by the proposed fabrication approach and custom elastomer. The first design focuses on springtail- and gecko-inspired hybrid microfiber adhesive, which has the multifunctionalities of side-surface liquid super-repellency, top-surface liquid super-repellency, and strong reversible adhesion features in a single fiber array. The second design primarily centers on octopus- and gecko-inspired hybrid adhesive, which exhibits the benefits of both octopus- and gecko-inspired microstructured adhesives for strong reversible adhesion on both wet and dry surfaces, such as skin. This fabrication approach could be used to produce many other 3D complex elastomeric structural adhesives for future real-world applications.Publication Metadata only 5-nj Femtosecond Ti3+:sapphire laser pumped with a single 1 W green diode(Iop Publishing Ltd, 2018) N/A; N/A; Department of Physics; Department of Physics; Muti, Abdullah; Kocabaş, Aşkın; Sennaroğlu, Alphan; PhD Student; Faculty Member; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 227753; 23851We report a Kerr-lens mode-locked, extended-cavity femtosecond Ti3+:sapphire laser directly pumped at 520 nm with a 1 W AlInGaN green diode. To obtain energy scaling, the short x-cavity was extended with a q-preserving multi-pass cavity to reduce the pulse repetition rate to 5.78 MHz. With 880 mW of incident pump power, we obtained as high as 90 mW of continuous-wave output power from the short cavity by using a 3% output coupler. In the Kerr-lens mode-locked regime, the extended cavity produced nearly transform-limited 95 fs pulses at 776 nm. The resulting energy and peak power of the pulses were 5.1 nJ and 53 kW, respectively. To our knowledge, this represents the highest pulse energy directly obtained to date from a mode-locked, single-diode-pumped Ti3+:sapphire laser.Publication Metadata only 80-NJ multipass-cavity chirped-pulse Cr4+: forsterite laser(Optical Society of America, 2010) Fujimoto, James G.; Department of Physics; Sennaroğlu, Alphan; Çankaya, Hüseyin; Faculty Member; Researcher; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; 23851; N/ABy using 8.5 W of incident pump power, we obtained 80-nJ, 5.5-ps pulses at 1260 nm with a spectral width of 17 nm from a multipass-cavity, chirped-pulse Cr4+:forsterite laser operated at 4.9-MHz repetition rate. © 2010 Optical Society of America.Publication Open Access A broken gauge approach to gravitational mass and charge(Springer, 2002) Tucker, R. W.; Department of Physics; Dereli, Tekin; Faculty Member; Department of Physics; College of Sciences; 201358We argue that a spontaneous breakdown of local Weyl invariance offers a mechanism in which gravitational interactions contribute to the generation of particle masses and their electric charge. The theory is formulated in terms of a spacetime geometry whose natural connection has both dynamic torsion and non-metricity. Its structure illuminates the role of dynamic scales used to determine measurable aspects of particle interactions and it predicts an additional neutral vector boson with electroweak properties. © SISSA/ISAS 2002.Publication Metadata only A communication theoretical modeling of single-layer graphene photodetectors and efficient multireceiver diversity combining(Ieee-Inst Electrical Electronics Engineers Inc, 2012) N/A; Department of Electrical and Electronics Engineering; Gülbahar, Burhan; Akan, Özgür Barış; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; 234525; 6647Graphene with groundbreaking properties has tremendous impact on physical sciences as 2-D atomic layer carbon sheet. Its unique electronic and photonic properties lead to applications such as transistors, graphene photodetectors (GPDs), and electronic circuit components. Metal-graphene-metal (MGM) GPDs with single-or multilayer graphene sheets are promising for future nanoscale optical communication architectures because of wide range absorption from far infrared to visible spectrum, fast carrier velocity, and advanced production techniques due to planar geometry. In this paper, signal-to-noise ratio (SNR), bit-error rate (BER), and data rate performances of nanoscale single-layer symmetric MGM photodetectors are analyzed for intensity modulation and direct detection (IM/DD) modulation. Shot and thermal noise limited (NL) performances are analyzed emphasizing graphene layer width dependence and domination of thermal NL characteristics for practical power levels. Tens of Gbit/s data rates are shown to be achievable with very low BERs for single-receiver (SR) GPDs. Furthermore, multireceiver (MR) GPDs and parallel line-scan (PLS) network topology are defined improving the efficiency of symmetric GPDs. SNR performance of SR PLS channels are both improved and homogenized with MR devices having the same total graphene area by optimizing their positions with maxmin solutions and using maximal ratio and equal gain diversity combining techniques.Publication Metadata only A communication theoretical modeling of single-walled carbon nanotube optical nanoreceivers and broadcast power allocation(Ieee-Inst Electrical Electronics Engineers Inc, 2012) N/A; Department of Electrical and Electronics Engineering; Gülbahar, Burhan; Akan, Özgür Barış; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; 234525; 6647Carbon nanotube (CNT) with its ground-breaking properties is a promising candidate for future nanoscale communication networks. CNTs can be used as on-chip optical antenna for wireless interconnects. Carbon nanotube field-effect transistors (CNTFETs) show significant performance as photodetectors due to wide spectral region and tunable bandgap. In this paper, CNTFETs composed of semiconducting single-walled carbon nanotube (SWNT) and metal contacts (M-SWNT-M) are used as photodiode receivers in nanoscale optical communication by theoretically modeling diameter-dependent characteristics for shot-, dark-, and thermal-noise-limited cases. Bit error rate (BER), cutoff bit rate, and signal-to-noise ratio performance are analyzed for intensity modulation and direct detection modulation. The multireceiver CNT nanoscale network topology is presented for information broadcast and the minimum SNR is maximized solving NP-hard max-min power allocation problem with semidefinite programming relaxation and branch and bound framework. The significant performance improvement is observed compared with uniform power allocation. Derived model is compared with existing experiments and hundreds of Mb/s data rate is achievable with very low BERs. Furthermore, optimization gain is highest for thermal-noise-limited case while the shot-noise-limited case gives the highest data rate.Publication Open Access A comparative study on GaSb epilayers grown on nominal and vicinal Si(100) substrates by molecular beam epitaxy(Institute of Physics (IOP) Publishing, 2020) Arpapay, Burcu; Suyolcu, Y. Eren; van Aken, Peter A.; Gülgün, Mehmet Ali; Serincan, Uğur; Çorapçıoğlu, Gülcan; n2STAR-Koç University Nanofabrication and Nanocharacterization Center for Scientifc and Technological Advanced ResearchThe direct growth of GaSb buffer layers on Si substrates is attracting considerable interest in the integration of group III-Sb based device structures on lower-cost Si substrates. Here, we present the effect of various growth steps on the defect types and defect density that are crucial for advancing high crystal quality GaSb buffer layer on nominal/vicinal Si substrate. As a growth step, the applied thermal annealing at an intermediate step provided a decrease in the threading dislocation (TD) density down to 1.72 x 10(8) cm(-2), indicating a more effective method compared to post-growth annealing. Additionally, the importance of period number and position of GaSb/AlSb superlattice layers inserted in GaSb epilayers is demonstrated. In the case of the GaSb epilayers grown on vicinal substrates, the APB density as low as 0.06 mu m(-1) and TD density of 1.98 x 10(8) cm(-2) were obtained for the sample grown on 4 degrees miscut Si(100) substrate.