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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6

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Quartile: search.filters.quartile.Q3Subject: search.filters.subject.Nanoscience and nanotechnology

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Now showing 1 - 4 of 4
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    PublicationOpen Access
    Hydrothermal-electrochemical growth of heterogeneous zno: co films
    (SpringerOpen, 2017) Department of Chemistry; Akkaya, Ceren Yılmaz; Ünal, Uğur; PhD Student; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering
    BACKGROUND: Central venous cannulation is a necessary invasive procedure for fluid management, haemodynamic monitoring and vasoactive drug therapy. The right internal jugular vein (RIJV) is the preferred site. Enlargement of the jugular vein area facilitates catheterization and reduces complication rates. Common methods to enlarge the RIJV cross-sectional area are the Trendelenburg position and the Valsalva maneuver. OBJECTIVE: Compare the Trendelenburg position with upper-extremity venous return blockage using the tourniquet technique. DESIGN: Prospective clinical study. SETTING: University hospital. SUBJECTS AND METHODS: Healthy adult volunteers (American Society of Anesthesiologists class I) aged 18-45 years were included in the study. The first measurement was made when the volunteers were in the supine position. The RIJV diameter and cross-sectional area were measured from the apex of the triangle formed by the clavicle and the two ends of the sternocleidomastoid muscle, which is used for the conventional approach. The second measurement was performed in a 20 degrees Trendelenburg position. After the drainage of the veins using an Esbach bandage both arms were cuffed. The third measurement was made when tourniquets were inflated. MAIN OUTCOME MEASURE(S): Hemodynamic measurements and RIJV dimensions. RESULTS: In 65 volunteers the diameter and cross-sectional area of the RIJV were significantly widened in both Trendelenburg and tourniquet measurements compared with the supine position (P<.001 for both measures). Measurements using the upper extremity tourniquet were significantly larger than Trendelenburg measurements (P=.002 and <.001 for cross-sectional area and diameter, respectively). CONCLUSION: Channelling of the upper-extremity venous return to the jugular vein was significantly superior when compared with the Trendelenburg position and the supine position. LIMITATIONS: No catheterization and study limited to healthy volunteers.
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    PublicationOpen Access
    An information theoretical analysis of nanoscale molecular gap junction communication channel between cardiomyocytes
    (Institute of Electrical and Electronics Engineers (IEEE), 2013) Kılınç, Deniz; Akan, Özgür Barış; College of Engineering
    Molecular communication (MC) is a promising paradigm to communicate at nanoscale and it is inspired by nature. One of the MC methods in nature is the gap junction (GJ) communication between cardiomyocytes. The GJ communication is achieved by diffusion of ions through GJ channels between the cells. The transmission of the information is realized by means of the propagation of the action potential (AP) signal. The probabilities of both the AP propagation failure and the spontaneous AP initiation are obtained. For the first time in the literature, the GJ communication channel is modeled and analyzed from the information theoretical perspective to find the communication channel capacity. A closed-form expression is derived for the capacity of the GJ communication channel. The channel capacity, propagation delay, and information transmission rate are analyzed numerically for a three-cell network. The results of the numerical analyses point out a correlation between an increase in the incidence of several cardiac diseases and a decrease in the channel capacity, an increase in the propagation delay, and either an increase or a decrease in the transmission rate. The method that we use and results that are presented may help in the investigation, diagnosis, and treatment of cardiac diseases as well as help in the design of nanodevices communicating via GJ channels.
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    PublicationOpen Access
    Communicate to illuminate: state-of-the-art and research challenges for visible light communications
    (Elsevier, 2015) Ergül, Özgür; Dinç, Ergin; Akan, Özgür Barış; PhD Student; PhD Student; College of Engineering
    In the near future, the available radio-frequency (RF) bandwidth will not be sufficient to meet the ever increasing demand for wireless access. Visible light communication (VLC) is an alternative method to reduce the burden of RF-based communication, especially in indoor communications. 70% of the communication is indoors, and light emitting diode (LED) arrays are spreading for illumination purposes thanks to their low energy and higher lifetime. VLC can be realized as a secondary application in LED arrays that are placed for lighting. In this way, some of the wireless traffic can be sent using light, with less cost and less carbon footprint. For these reasons, VLC attracts significant research interests. We provide an extensive survey of the current literature by outlining challenges and future research areas in order to facilitate future research in this area.
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    PublicationOpen Access
    A physical channel model and analysis for nanoscale molecular communications with Förster resonance energy transfer (FRET)
    (Institute of Electrical and Electronics Engineers (IEEE), 2012) Kuşcu, Murat; Akan, Özgür Barış; Faculty Member; College of Engineering
    In this study, a novel and physically realizable nanoscale communication paradigm is introduced based on a well-known phenomenon, Forster resonance energy transfer (FRET), for the first time in the literature. FRET is a nonradiative energy transfer process between fluorescent molecules based on the dipole-dipole interactions of molecules. Energy is transferred rapidly from a donor to an acceptor molecule in a close proximity such as 0 to 10 nm without radiation of a photon. Low dependence on the environmental factors, controllability of its parameters, and relatively wide transfer range make FRET a promising candidate to be used for a high-rate nanoscale communication channel. In this paper, the simplest form of the FRET-based molecular communication channel comprising a single transmitter-receiver nanomachine pair and an extended version of this channel with a relay nanomachine for long-range applications are modeled considering nanomachines as nanoscale electromechanical devices with some sensing, computing, and actuating capabilities. Furthermore, using the information theoretical approach, the capacities of these communication channels are investigated and the dependence of the capacity on some environmental and intrinsic parameters is analyzed. It is shown that the capacity can be increased by appropriately selecting the donor-acceptor pair, the medium, the intermolecular distance, and the orientation of the molecules.