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Istanbul, Turkey

Subasi M.G.,Istanbul Aydin University | Inan O.,Selcuk University
Lasers in Medical Science

This study aimed to evaluate the surface changes caused in zirconia by different surface treatments and the influence of the surface treatment and cement selection on bonding to zirconia under aging. Sintered zirconia specimens were divided into five groups (n = 31) based on the surface treatment, namely, control, air abrasion, silica coating, laser and air abrasion + laser. After surface treatment, surface roughness and microscope analyses were performed on one specimen of each group. Composite cylinders were then bonded to conditioned ceramics using RelyX U100 (RXU), Clearfil Esthetic Cement (CEC) and Panavia F (PF) (n = 10). After 24 h, the bonded specimens were subjected to thermal cycling (6,000 times), and then, a shear bond strength test was conducted. The roughness values were analysed using Kruskal-Wallis and Mann-Whitney U tests, and the bond strengths were analysed by two-way analysis of variance and Duncan's test. The relationship between the roughness and the bond strength was determined by Spearman's correlation analysis. Specimens subjected to surface treatments were rougher than the control specimen (p < 0.000). However, there were no significant differences between the air abrasion and air abrasion + laser groups and the silica coating and laser groups. Specimens treated with laser showed lower bond strengths irrespective of the resin cement used. CEC and/or PF showed higher bond strengths than RXU for each surface treatment group. No significant relationship was observed between the roughness and the bond strength. The results of this study showed that all the surface treatments, except for laser irradiation, were suitable for treating zirconia ceramics. Cement selection was found to be more important than surface treatment, and phosphate monomer-containing cements were suitable for cementing zirconia. © 2012 Springer-Verlag London. Source

Kocak Y.,Dumlupinar University | Nas S.,Istanbul Aydin University
Construction and Building Materials

The present study is aimed at investigating the combined effects of the compressive strength and hydration development of blended cements which contain fly ash. In the first stage, chemical, physical, X-Ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FT-IR) analysis were performed in order to determine the characteristics of Portland cement and fly ash. In the second stage, the compressive strength of cement mortars and setting time, water demand and volume expansion of cement pastes were identified according to the standard cement experiments. In the last stage, XRD, FT-IR, thermal and scanning electron microscope analyses were performed in order to determine the hydration of cement pastes. Consequently, the addition of FA in Portland cement contributes to the consumption of Ca(OH)2 which is formed during the hydration of cement and leads to the formation of cementitious products, like C-S-H. Therefore, the compressive strength of fly ash blended cement mortars increased at later ages compared to the early ages. © 2014 Elsevier Ltd. Source

Kasapbasi E.E.,Istanbul Aydin University | Whangbo M.-H.,North Carolina State University
Inorganic Chemistry

Recently it was discovered that the iron coordination complex L N4Fe(II)(OTf)2 (1) (LN4 = neutral tetraazadendate ligand and OTf = OSO2CF3) and its analogues are efficient water oxidizing catalysts (WOCs) in aqueous acidic solution with excess amount of ceric(IV) ammonium nitrate (CAN), [Ce(IV)(NO 3)6](NH4)2, as sacrificial oxidants. The probable mechanism of water oxidation by these catalysts was explored on the basis of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations for 1 as a representative WOC. We examined the conversion of 1 to the resting intermediate [LN4Fe(IV)(O)(OH2)]2+ [2(IV)] as well as two catalytic cycles involving 2(IV): one proposed by Fillol et al. [Nat. Chem. 2011, 3, 1] in which the Fe oxidation states of the intermediate species vary from +2 to +5, and the alternative cycle in which they remain constant at +4. In addition, we investigated the role of the sacrificial oxidant CAN in driving the catalytic cycle. Our DFT and TD-DFT calculations confirm the experimental observation that 2(IV) is the resting species, and indicate that the catalytic cycle in which the Fe oxidation states of the intermediate species remain at +4 is energetically more favorable. © 2012 American Chemical Society. Source

Demir M.A.,Istanbul Aydin University | Johnson J.T.,Ohio State University | Zajdel T.J.,Ohio State University
IEEE Transactions on Geoscience and Remote Sensing

Predictions of the fourth-order small perturbation method (SPM) are examined for scattering from two rough surfaces in a layered geometry. Cross-polarized backscatter, in particular, is emphasized because use of the fourth-order SPM is required to obtain this quantity. The formulation of the SPM fields and incoherent ensemble-averaged normalized radar cross sections (NRCSs) up to the third and the fourth order in surface rms heights, respectively, are reviewed. It is shown that the fourth-order NRCS includes distinct contributions from upper and lower interface roughnesses, as well as an " interaction" term that couples the upper and lower interface roughnesses. A comparison with NRCS values computed using the "numerically exact" method of moments in the full bistatic scattering pattern is shown for verification, and NRCS values at the second and the fourth order are compared in order to assess the convergence of the SPM series. Although the number of parameters inherent in the two-layer rough surface scattering problem makes an exhaustive study of scattering effects difficult, several illustrative examples are presented to capture a range of scattering behaviors. The results emphasize the importance of interactions between the rough surfaces in producing cross-polarized backscattering and also indicate an increased significance of fourth-order contributions in the two-layer geometry as compared to the single-layer case. © 2012 IEEE. Source

The temperature dependence of the bulk modulus of ZrB2 above room temperature was calculated by using the equations by Garai and Laugier (J. Appl. Phys. 101 (2007) p.023514) and Lawson and Ledbetter (Philos Mag. 91 (2011) p.1425). The present calculations involve the accurate data for pressure derivative of the bulk modulus for the Anderson-Grüneisen parameter in addition to the other experimental parameters involved. It is interesting to note that the cited equations derived by different thermodynamic approaches give almost equivalent values for the temperature dependencies of the bulk modulus of ZrB2. The present results for the temperature derivatives of the bulk modulus of ZrB2 vary from -0.016 GPa/K at 300-400 K to -0.022 GPa/K at 1500-1600 K, being in good agreements with the corresponding experimental values. © 2013 Taylor & Francis. Source

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