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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open 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 EngineeringBACKGROUND: 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.Publication Open Access Doping-induced isotopic (MgB2)-B-11 bulk superconductor for fusion application(Multidisciplinary Digital Publishing Institute (MDPI), 2017) Cai, Qi; Guo, Qianying; Liu, Yongchang; Ma, Zongqing; Li, Huijun; Qiu, Wenbin; Patel, Dipak; Jie, Hyunseock; Kim, Jung Ho; Yanmaz, Ekrem; Devred, Arnaud; Luzin, Vladimir; Fatehmulla, Amanullah; Farooq, Wazirzada Aslam; Gajda, Daniel; Bando, Yoshio; Yamauchi, Yusuke; Pradhan, Subrata; Hossain, Md. Shahriar A.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Superconducting wires are widely used for fabricating magnetic coils in fusion reactors. Superconducting magnet system represents a key determinant of the thermal efficiency and the construction/operating costs of such a reactor. In consideration of the stability of B-11 against fast neutron irradiation and its lower induced radioactivation properties, MgB2 superconductor with B-11 serving as the boron source is an alternative candidate for use in fusion reactors with a severe high neutron flux environment. In the present work, the glycine-doped (MgB2)-B-11 bulk superconductor was synthesized from isotopic B-11 powder to enhance the high field properties. The critical current density was enhanced (10(3) Acm(-2) at 20 K and 5 T) over the entire field in contrast with the sample prepared from natural boron.Publication Open Access Evolution of magnetic properties of crystalline cobalt-iron boride nanoparticles via optimization of synthesis conditions using hydrous metal chlorides(Elsevier, 2021) Schmidt, Marcus; Bobnar, Matej; Burkhardt, Ulrich; Department of Chemistry; Altıntaş, Zerrin; Khoshsima, Sina; Somer, Mehmet Suat; Researcher; Researcher; Researcher; Department of Chemistry; Koç University AKKİM Boron-Based Materials _ High-technology Chemicals Research _ Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); College of Sciences; N/A; N/A; 295531Chemical synthesis of crystalline and nanoscale cobalt-iron metal boride powders was studied using hydrous metal chlorides and NaBH4. The effects of precursor concentration and optimized synthesis conditions on the phase formation, microstructure, and magnetic properties were investigated. After applying a reaction of CoCl2·6H2O-FeCl3·6H2O-NaBH4 at 850 °C, (CoFe)B2, (CoFe)B, Co2B, Fe3B, and Fe0.71Co0.29 boride phases were obtained from different synthesis conditions applied under autogenic pressure or Ar flow atmosphere. Oxychloride impurities were the reason for the reduced magnetization values. The highest saturation magnetization of 183 emu/g belongs to obtained nanoparticles containing (CoFe)B2 and (CoFe)B pure phases. High temperature magnetic measurements marked synthesized powders as soft magnetic materials up to 795 K while no Tc was reached for the obtained phases.Publication Open Access Quenching vibrations by collisions in cold traps: A quantum study for MgH+ (X-1 Sigma(+)) with He-4(S-1)(Indian Academy of Sciences, 2012) Caruso, Domenico; Tacconi, Mario; Gianturco, Franco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Quantum dynamics of superelastic collisions involving vibrational levels of MgH+ (X-1 Sigma(+)) ions in cold traps, interacting with He-4(S-1) as a buffer gas at relative temperatures down to millikelvins, is discussed using an ab initio computed potential energy surface. The relative efficiency of collisional cooling with respect to collisional quenching of the internal vibrations is examined from the results of the relative sizes of the relevant cross sections in relation to predicting actual behaviour in cold traps. The present study indicates the feasibility of cooling vibrationally 'hot', trapped ions with the buffer gas.Publication Open Access Collisional relaxation kinetics for ortho and para NH2- under photodetachment in cold ion traps(Royal Society of Chemistry (RSC), 2018) Gianturco, Francesco A.; Lakhmanskaya, Olga Y.; Vera, Mario Hernandez; Wester, Roland; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The collisional cooling of the internal rotational states of the nonlinear anion NH2- ((1)A(1)), occurring at the low temperature of a cold ion trap under helium buffer gas cooling, is examined via quantum dynamics calculations and ion decay rate measurements. The calculations employ a novel ab initio potential energy surface that describes the interaction anisotropy and range of action between the molecular anions and the neutral He atoms. The state changing integral cross sections are employed to obtain the state-to-state rate coefficients, separately for the ortho- and the para-NH2- ions. These rates are in turn used to compute the state population evolution in the trap for both species, once photodetachment by a laser is initiated in the trap. The present work shows results for the combined losses of both species after the photodetachment laser is switched on and analyzes the differences of loss kinetics between the two hyperfine isomers.Publication Open Access Thermalisation of C2− with noble gases in cold ion traps(Elsevier, 2020) Mant, Barry P.; Gianturco, Franco A.; Wester, Roland; Gonzalez-Sanchez, Lola; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The potential energy surfaces for C2− (Σg+2) interacting with He, Ne and Ar are calculated using ab initio quantum chemistry methods. The PES are used to carry out coupled-channel quantum scattering calculations for the three systems to obtain the rotationally inelastic scattering cross sections from which the rotationally inelastic state-changing rate coefficients are computed. These rate coefficients are then used to compute thermalisation times of C2− in an ion trap employing He, Ne or Ar as different, and possible, buffer gases. A detailed analysis of their comparative collisional efficiencies is presented for guidance in trap modeling studies.