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Quartile: search.filters.quartile.Q2Subject: search.filters.subject.Applied physics

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Now showing 1 - 10 of 28
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    PublicationOpen Access
    3D printed microneedles for point of care biosensing applications
    (Multidisciplinary Digital Publishing Institute (MDPI), 2022) Department of Mechanical Engineering; Sarabi, Misagh Rezapour; Nakhjavani, Sattar Akbar; Taşoğlu, Savaş; Faculty Member; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Koç Üniversitesi İş Bankası Yapay Zeka Uygulama ve Araştırma Merkezi (KUIS AI)/ Koç University İş Bank Artificial Intelligence Center (KUIS AI); Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 291971
    Microneedles (MNs) are an emerging technology for user-friendly and minimally invasive injection, offering less pain and lower tissue damage in comparison to conventional needles. With their ability to extract body fluids, MNs are among the convenient candidates for developing biosensing setups, where target molecules/biomarkers are detected by the biosensor using the sample collected with the MNs. Herein, we discuss the 3D printing of microneedle arrays (MNAs) toward enabling point-of-care (POC) biosensing applications.
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    Aerogels for optofluidic waveguides
    (MDPI, 2017) Jonas, Alexandr; N/A; Department of Physics; Department of Chemical and Biological Engineering; Özbakır, Yaprak; Erkey, Can; Kiraz, Alper; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; 29633; 22542
    Aerogels-solid materials keeping their internal structure of interconnected submicron-sized pores intact upon exchanging the pore liquid with a gas-were first synthesized in 1932 by Samuel Kistler. Overall, an aerogel is a special form of a highly porous material with a very low solid density and it is composed of individual nano-sized particles or fibers that are connected to form a three-dimensional network. The unique properties of these materials, such as open pores and high surface areas, are attributed to their high porosity and irregular solid structure, which can be tuned through proper selection of the preparation conditions. Moreover, their low refractive index makes them a remarkable solid-cladding material for developing liquid-core optofluidic waveguides based on total internal reflection of light. This paper is a comprehensive review of the literature on the use of aerogels for optofluidic waveguide applications. First, an overview of different types of aerogels and their physicochemical properties is presented. Subsequently, possible techniques to fabricate channels in aerogel monoliths are discussed and methods to make the channel surfaces hydrophobic are described in detail. Studies in the literature on the characterization of light propagation in liquid-filled channels within aerogel monoliths as well as their light-guiding characteristics are discussed. Finally, possible applications of aerogel-based optofluidic waveguides are described.
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    PublicationOpen Access
    Al-doped MgB2 materials studied using electron paramagnetic resonance and Raman spectroscopy
    (American Institute of Physics (AIP) Publishing, 2016) Erdem, Emre; Repp, Sergej; Weber, Stefan; N/A; Department of Chemistry; Bateni, Ali; Somer, Mehmet Suat; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882
    Undoped and aluminum (Al) doped magnesium diboride (MgB2) samples were synthesized using a high-temperature solid-state synthesis method. The microscopic defect structures of Al-doped MgB2 samples were systematically investigated using X-ray powder diffraction, Raman spectroscopy, and electron paramagnetic resonance. It was found that Mg-vacancies are responsible for defect-induced peculiarities in MgB2. Above a certain level of Al doping, enhanced conductive properties of MgB2 disappear due to filling of vacancies or trapping of Al in Mg-related vacancy sites. Published by AIP Publishing.
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    Automatic CNN-based Arabic numeral spotting and handwritten digit recognition by using deep transfer learning in Ottoman population registers
    (Mdpi, 2020) N/A; Department of History; Can, Yekta Said; Kabadayı, Mustafa Erdem; Researcher; Faculty Member; Department of History; College of Social Sciences and Humanities; College of Social Sciences and Humanities; N/A; 33267
    Historical manuscripts and archival documentation are handwritten texts which are the backbone sources for historical inquiry. Recent developments in the digital humanities field and the need for extracting information from the historical documents have fastened the digitization processes. Cutting edge machine learning methods are applied to extract meaning from these documents. Page segmentation (layout analysis), keyword, number and symbol spotting, handwritten text recognition algorithms are tested on historical documents. For most of the languages, these techniques are widely studied and high performance techniques are developed. However, the properties of Arabic scripts (i.e., diacritics, varying script styles, diacritics, and ligatures) create additional problems for these algorithms and, therefore, the number of research is limited. In this research, we first automatically spotted the Arabic numerals from the very first series of population registers of the Ottoman Empire conducted in the mid-nineteenth century and recognized these numbers. They are important because they held information about the number of households, registered individuals and ages of individuals. We applied a red color filter to separate numerals from the document by taking advantage of the structure of the studied registers (numerals are written in red). We first used a CNN-based segmentation method for spotting these numerals. In the second part, we annotated a local Arabic handwritten digit dataset from the spotted numerals by selecting uni-digit ones and tested the Deep Transfer Learning method from large open Arabic handwritten digit datasets for digit recognition. We achieved promising results for recognizing digits in these historical documents.
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    PublicationOpen Access
    Controlled photoluminescence in amorphous-silicon-nitride microcavities
    (American Institute of Physics (AIP) Publishing, 2001) Tanrıseven, S.; Department of Physics; Serpengüzel, Ali; Faculty Member; Department of Physics; College of Sciences; 27855
    Narrow-band and enhanced photoluminescence have been observed in hydrogenated amorphous-silicon-nitride microcavities. The distributed Bragg reflectors were fabricated using alternating layers of hydrogenated amorphous-silicon nitride and hydrogenated amorphous-silicon oxide. The microcavity resonance wavelength was designed to be at the maximum of the bulk hydrogenated amorphous-silicon-nitride luminescence spectrum. At the microcavity resonance, the photoluminescence amplitude is enhanced, while the photoluminescence linewidth is reduced with respect to the bulk hydrogenated amorphous-silicon nitride. (C) 2001 American Institute of Physics.
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    PublicationOpen Access
    Defect structure of ultrafine MgB2 nanoparticles
    (American Institute of Physics (AIP) Publishing, 2014) Repp, Sergej; Thomann, Ralf; Acar, Selçuk; Erdem, Emre; N/A; Department of Chemistry; Bateni, Ali; Somer, Mehmet Suat; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882
    Defect structure of MgB2 bulk and ultrafine particles, synthesized by solid state reaction route, have been investigated mainly by the aid of X-band electron paramagnetic resonance spectrometer. Two different amorphous Boron (B) precursors were used for the synthesis of MgB2, namely, boron 95 (purity 95%-97%, <1.5 mu m) and nanoboron (purity >98.5%, <250 nm), which revealed bulk and nanosized MgB2, respectively. Scanning and transmission electron microscopy analysis demonstrate uniform and ultrafine morphology for nanosized MgB2 in comparison with bulk MgB2. Powder X-ray diffraction data show that the concentration of the by-product MgO is significantly reduced when nanoboron is employed as precursor. It is observed that a significant average particle size reduction for MgB2 can be achieved only by using B particles of micron or nano size. The origin and the role of defect centers were also investigated and the results proved that at nanoscale MgB2 material contains Mg vacancies. Such vacancies influence the connectivity and the conductivity properties which are crucial for the superconductivity applications. (C) 2014 AIP Publishing LLC.
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    PublicationOpen Access
    Dielectric response and tunability of a dielectric-paraelectric composite
    (American Institute of Physics (AIP) Publishing, 2008) Zhou, K.; Boggs, S. A.; Ramprasad, R.; Aindow, M.; Alpay, S. P.; Department of Chemical and Biological Engineering; Erkey, Can; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 29633
    A theoretical study was carried out to determine the dielectric response and tunability of a composite consisting of a linear, low-loss dielectric matrix with uniformly sized, randomly distributed paraelectric Ba0.60Sr0.40TiO3 (BST 60/40) particles as functions of the volume fraction and size of the particles. The field dependence of the polarization and the dielectric response of the inclusions are specified through a nonlinear thermodynamic model and then incorporated into a two-dimensional finite element analysis. Near the percolation threshold for BST particles (similar to 27% to 45% depending on the particle size), high dielectric tunabilities with a lower effective permittivity than monolithic BST can be realized. (C) 2008 American Institute of Physics. American Institute of Physics.
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    PublicationOpen Access
    Electron paramagnetic resonance and Raman spectroscopy studies on carbon-doped MgB2 superconductor nanomaterials
    (American Institute of Physics (AIP) Publishing, 2015) Erdem, Emre; Repp, Sergej; Acar, Selçuk; Kokal, İlkin; Haessler, Wolfgang; Weber, Stefan; N/A; Department of Chemistry; Bateni, Ali; Somer, Mehmet Suat; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882
    Undoped and carbon-doped magnesium diboride (MgB2) samples were synthesized using two sets of mixtures prepared from the precursors, amorphous nanoboron, and as-received amorphous carbon-doped nanoboron. The microscopic defect structures of carbon-doped MgB2 samples were systematically investigated using X-ray powder diffraction, Raman and electron paramagnetic resonance spectroscopy. Mg vacancies and C-related dangling-bond active centers could be distinguished, and sp(3)-hybridized carbon radicals were detected. A strong reduction in the critical temperature T-c was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra. (C) 2015 AIP Publishing LLC.
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    PublicationMetadata only
    Electronic and optical properties of stanane and armchair stanane nanoribbons
    (Springer Heidelberg, 2020) Dideban, Daryoosh; Gulseren, Oguz; N/A; N/A; N/A; N/A
    In this study, we performed a density functional theory based investigation of the structural, electronic, and optical properties of a stanane, fully hydrogenated stanene SnH, and armchair stanane nanoribbons ASnHNRs. Our full geometry optimization calculations show stanane has 0.84 angstrom buckled height and the buckled structure is preserved in ASnHNRs. The optimized lattice parameter of stanane, Sn-Sn, and Sn-H bond length are 4.58 angstrom, 2.75 angstrom, and 1.73 angstrom, respectively. Electronic structure calculations show that stanane is a moderate-band-gap semiconductor with a direct band gap of 1.2 eV and ASnHNRs are wide-band-gap semiconductors. The band gap of ASnHNRs decreases as the ribbons width increases. We investigated the optical properties for two directions of polarization. For perpendicular-polarized light, the imaginary part of dielectric function epsilon 2(omega) of stanane peaks between 5 and 10 eV; while for the parallel-polarized light, the peaks are seen in a wide range of energy. According to the results, stanane is a good absorptive matter, especially for visible regions of the electromagnetic spectrum. The presence of anisotropy with respect to the type of light polarization is observed in ASnHNRs also. In these structures, the main peak of epsilon 2(omega) is located at 3.4 eV for parallel- and in 6-8 eV for perpendicular-polarized light.
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    PublicationOpen Access
    Field-effect active plasmonics for ultracompact electro-optic switching
    (American Institute of Physics (AIP) Publishing, 2012) Çetin, Arif E.; Yanık, Ahmet A.; Mertiri, Alket; Erramilli, Shyamsunder; Altuğ, Hatice; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674
    Merging of electronics and photonics at subwavelength dimensions could potentially allow development of ultracompact electro-optic modulators and active optical interconnects. Here, we introduce a field-effect active plasmonic modulator where the metallic ring serves as both a photonic resonator and a field electrode. By exploiting the simultaneous electronic and photonic functionalities of our plasmonic device, we show devices offering significantly improved modulation depths (as high as similar to 10.85 dB) compared to active dielectric micro-ring resonators. Device concepts introduced in this work are applicable in realization of various integrated components and could play an important role in development of active plasmonic circuits.