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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; Department of Chemistry; Akkaya, Ceren Yılmaz; Ünal, Uğur; PhD Student; Faculty Member; 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 Improved superconducting properties in the Mg11B2 low activation superconductor prepared by low-temperature sintering(Nature Publishing Group (NPG), 2016) F. Cheng, Y.; Liu, Z. Ma; Hossain, M. S.; Department of Chemistry; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; College of Sciences; 178882Mg11B2 has a great application prospect in the superconducting coils for fusion reactor as the “low activation superconductors”. The un-doped Mg11B2 and Cu-doped Mg11B2 bulks using 11B as a boron precursor were fabricated by low-temperature sintering in present work. It was found that the prepared Mg11B2 low activation superconductors exhibit better Jc performance than all of other Mg11B2 samples reported in previous studies. As for Cu doped Mg11B2, minor Cu addition can obviously improve the Mg11B2 grain crystallization and reduce the amount of MgO impurity. Hence, improved grain connectivity and higher Jc at low fields is obtained in Cu doped Mg11B2 samples. For un-doped samples, refined grains and more MgO impurity with proper size brought about more flux pinning centers, resulting in better Jc performance at high fields.Publication Open Access Failures of the discourse of ethnicity: Turkey, Kurds, and the emerging Iraq(Sage, 2005) Department of Chemistry; Department of Chemistry; Somer, Murat; Faculty Member; College of Sciences; 110135This article analyzes the discursive-ideational barriers restricting regional cooperation by examining Turkey's relations with Iraqi Kurds from a critical, theoretical perspective in the context of Turkey's domestic reforms and its relations with the USA and the EU. It is argued that the ethnicity discourse undermines cooperation, insofar as it feeds the perception of rival groups with zero-sum interests. Presenting a simple model, the article argues that replacing the ethnicity discourse with alternative, post-ethnic discourses requires combining alternative discourses with policies that produce positive-sum interests, coordination between groups, and opportunities for joint collective actions. Hence, state capacity to formulate and implement such policies is crucial. Predictions and policy implications are generated accordingly. First, further reconciliation of Turkey's domestic Kurdish conflict through democratic and administrative reforms, EU integration, and the promotion of national-identity models that are more flexible and more reflective of diversity will facilitate cooperation with Iraqi Kurds. Second, prosperity and democratic stability in Iraq will help achieve a lasting resolution in Turkey. Third, regional cooperation requires that domestic and external actors promote the positive-sum perception of Turkish and Kurdish interests. Fourth, research can help by developing linguistic-analytical categories that transcend the narrow discourse of ethnicity in favor of discourses that reflect multiple and compatible group belongings.Publication Open Access CdTe quantum dot sensitized hexaniobate nanoscrolls and their photoelectrochemical properties(Royal Society of Chemistry (RSC), 2012) Department of Chemistry; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Akkaya, Ceren Yılmaz; Acar, Havva Funda Yağcı; Ünal, Uğur; PhD Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; N/A; N/A; 178902; N/AWe have constructed hybrid quantum dot-layered niobate films with an electrophoretic deposition method. The structure and photoelectrochemical behaviour were demonstrated.Publication Open Access Weakening the strength of CO binding on subsurface alloyed Pt(111)(Elsevier, 2019) Ogasawara, Hirohito; Department of Chemistry; N/A; Department of Chemistry; Kaya, Sarp; Gürlek, Sezen; Panahi, Mohammad; Solati, Navid; Faculty Member; PhD Student; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Sciences; Graduate School of Sciences and Engineering; 116541; N/A; N/A; N/AThe interaction of CO with Pt/3d/Pt(111) subsurface alloys (3d: Ni, Co, Fe) was investigated by combination of vibrational spectroscopy and temperature programmed desorption. The binding strength of CO is significantly reduced on Pt/Fe/Pt(111) and Pt/Co/Pt(111) and is sorted in the following order: Pt >Ni > Co approximate to Fe. Our analysis shows that the 3d admetal is stable in the subsurface region and CO is linearly bonded to the atop sites of the Pt(111) surface. At high CO coverage, compressed structures are obtained. At low CO coverage, the desorption activation energy of CO (similar to 143 kJ/mol for Pt(111)) drops to 124 kJ/mol for Pt/Ni/Pt(111), and goes further down to 111 and 110 kJ/mol for Pt/Co/Pt(111) and Pt/Fe/Pt(111), respectively. The enhancement in the surface activity is attributed to the modified backdonation to the antibonding states of adsorbed CO due to the downshifted 5d-band center of Pt upon embedding 3d metals in the subsurface region.Publication Open Access Grain boundary engineering with nano-scale InSb producing high performance InxCeyCo4Sb12+z skutterudite thermoelectrics(Elsevier, 2017) Li, Han; Su, Xianli; Tang, Xinfeng; Zhang, Qingjie; Uher, Ctirad; Snyder, G. Jeffrey; Department of Chemistry; Department of Chemistry; Aydemir, Umut; Faculty Member; College of Sciences; 58403Thermoelectric semiconductors based on CoSb3 hold the best promise for recovering industrial or automotive waste heat because of their high efficiency and relatively abundant, lead-free constituent elements. However, higher efficiency is needed before thermoelectrics reach economic viability for widespread use. In this study, n-type InxCeyCo4Sb12+z skutterudites with high thermoelectric performance are produced by combining several phonon scattering mechanisms in a panoscopic synthesis. Using melt spinning followed by spark plasma sintering (MS-SPS), bulk InxCeyCo4Sb12+z alloys are formed with grain boundaries decorated with nano-phase of InSb. The skutterudite matrix has grains on a scale of 100-200 nm and the InSb nano-phase with a typical size of 5-15 nm is evenly dispersed at the grain boundaries of the skutterudite matrix. Coupled with the presence of defects on the Sb sublattice, this multi-scale nanometer structure is exceptionally effective in scattering phonons and, therefore, InxCeyCo4Sb12/InSb nano-composites have very low lattice thermal conductivity and high zT values reaching in excess of 1.5 at 800 K.Publication Open Access LiMg0.1Co0.9BO3 as a positive electrode material for Li-ion batteries(Royal Society of Chemistry (RSC), 2018) Afyon, Semih; Department of Chemistry; Department of Chemistry; Zor, Ceren; Somer, Mehmet Suat; Researcher; Faculty Member; College of Sciences; Graduate School of Sciences and Engineering; N/A; 178882LiCoBO3 could be a promising cathode material given the electronic and ionic conductivity problems are addressed. Here, Mg substitution in LiCoBO3 is employed to stabilise the structure and improve the electrochemical performance. LiMg0.1Co0.9BO3 is synthesised for the first time via sol-gel method and Mg substitution in the structure is verified by X-ray powder diffraction and energy dispersive X-ray analyses. The electrochemical properties are investigated by galvanostatic cycling and cyclic voltammetry tests. The composite electrode with conductive carbon (reduced graphite oxide and carbon black) delivers a first discharge capacity of 32 mA h g(-1) within a 4.7-1.7 voltage window at a rate of 10 mA g(-1). The cycling is relatively stable compared to the unsubstituted LiCoBO3. Mg substitution may enhance the electrochemical performance of borate-based electrode materials when combined with suitable electrode design techniques.Publication Open Access Dimerization of pyrrole(TÜBİTAK, 1998) Yurtsever, Mine; Department of Chemistry; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; College of Sciences; 7129Accurate ab-inito quantum mechanical calculations of pyrrole dimers are reported. The thermodynamical stabilities of dimers with alpha - alpha, alpha -beta, and beta - beta type linkages are compared in order to predict the possibilities of branching in polypyrroles. Calculations employing large basis sets and including electron correlation effects predict the alpha - alpha dimers as the most stable form. However, an alpha - beta type bonding requires only 1.5-2.0 kcal/mol, and the energy necessary to introduce a beta - beta type bond is 3.6-4.0 kcal/mol. These values show that a high degree of branching is possible even at room temperatures.Publication Open Access Development of highly luminescent and cytocompatible near-IR-emitting aqueous Ag2S quantum dots(Royal Society of Chemistry (RSC), 2012) Çizmeciyan, M. Natali; Erdem, Rengin; Özen, Can; Kurt, Adnan; N/A; Department of Physics; Department of Chemistry; Department of Physics; Department of Chemistry; Hocaoğlu, İbrahim; Sennaroğlu, Alphan; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851; 178902Colloidally stable and highly luminescent near-IR emitting Ag2S quantum dots (NIRQDs) were prepared by a very simple aqueous method using 2-mercaptopropionic acid (2MPA) as a coating. Emission of Ag2S-2MPA NIRQDs can be tuned between 780 and 950 nm. These NIRQDs have photoluminescence quantum yields (PLQY) around 7–39% and exhibit excellent cytocompatibility even at 600 mg mL 1 in NIH/3T3 cells. With such improved properties, Ag2S-2MPA NIRQDs have a great potential in practical bio-applications.Publication Open 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; Department of Chemistry; Bateni, Ali; Somer, Mehmet Suat; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178882Undoped 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.