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    A comparative investigation for identification of N-(4-dimethylamino 3,5-dinitrophenyl)maleimide
    (2023) Karaboğ, Seda; Yildirim, Gürcan
    This study has identified the characteristic behaviors of N-(4-dimethylamino 3,5-dinitrophenyl)maleimide molecule using ab initio Hartree-Fock (HF) and density functional theory (DFT) based on Becke’s three-parameter hybrid exchange functional combined with Lee-Yang-Parr non-local correlation function (HF/B3LYP and DFT/B3LYP) at 6-311G++(d,p) level of theory for the first time. On this basis, the optimized molecular structures, some thermodynamic features at 300 K, function groups of structures, charge distributions-dipole moments, molecular charge transfer regions, spectroscopic characteristic properties, vibrational frequencies, nuclear magnetic resonance chemical shifts of 13C-NMR and 1H-NMR spectra, and corresponding vibrational assignments have been investigated in detail. Comparisons between some experimental findings and theoretical results are performed to test the reliability of the calculation method preferred in the study. The comparison results in high correlation parameters such as R2 =0.976 and R2 =0.985 for the molecular structures and vibrational frequencies in the DFT and HF calculation levels, respectively. Moreover, the obtained vibrational frequencies and calculated results are in good agreement with the experimental data. Additionally, the simulations of highest/lowest occupied/unoccupied molecular orbital (HOMO and LUMO), molecular electrostatic potential (MEP), and electrostatic potential (ESP) maps have shown that there appear strong non-uniform intra-molecular charge distributions (ICT), electron engagements, lone pairs of electrons, ?-?* conjugative effects based on the bond weakening, and intermolecular hydrogen bonding in the compound. Correspondingly, the molecule with the electrophilic reactive and nucleophilic regions has been noted to exhibit kinetical chemical stability. All the discussions have been confirmed by means of the findings of optimized molecular structures and vibrational frequencies belonging to the molecule.
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    Determination of Possible Maximum Critical Transition Temperatures with Empirical Model Depending on Structural Disorders-Defects for $Bi_{2.1}Sr_{2.0}Ca_{1.1}Cu_{2.0}O_y$ System
    (2021) Erdem, Ümit; Yildirim, Gürcan
    In this study, we find a strong link depending on the preparation annealing ambient conditions between structural disorders-defects and characteristic transition temperature parameters $(offset, T_c ^{offset} and onset, T_c ^{offset})$ of bulk $Bi_{2.1}Sr_{2.0}Ca_{1.1}Cu_{2.0}O_y$ system for the first time. The superconducting samples are prepared at various annealing temperatures intervals 830°C -850°C with the temperature step of 10°C for annealing time ranging between 24 h and 48 h via traditional solid-state reaction route. The temperature-dependent resistivity measurements are conducted at temperature range of 30-140 K. The most ideal annealing ambient is obtained to be the combination of annealing temperature of 840 °C and annealing time of 24 h because of the enhancement in the formation possibility of strong cooper-pairs and optimization of itinerant charge carrier concentrations in the valence band. Similarly, the positive contributions are observed in the overlapping mechanism of wave functions between Cu-3d and O-2p electrons and especially logarithmic distribution of electronic state densities. The optimum annealing ambient makes the Bi-2212 system refine the structural problems and especially connectivity between the grains in the crystal structure. Conversely, the excess annealing ambient leads to increase considerably the grain misorientation, defects and grain boundary couplings due to the induced permanent problems in the crystal system. The highest correlated model shows that the Bi-2212 superconducting compounds with the minimum structural disorders in the short-range-ordered antiferromagnetic $Cu-O_2$ layers exhibit the maximum $T_c ^{offset} and T_c ^{offset}$ values of about 85.347 K (R2adj=0.9882) and 87.421 K (R2adj=0.97465).
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    EXAMINATION OF VANADIUM EFFECT ON GENERAL MECHANICAL CHARACTERISTICS OF Bi-2223 MATERIALS VIA SEMI-EMPIRIC MODELS
    (2020) Soykan, Uğur; Veliyeva, Fidan; Yildirim, Gürcan
    In the current work, we semi-empirically investigate the load-independent Vickers hardness values of vanadium added Bi2223 compounds in the plateau limit regions evaluated from the experimental microhardness graphics (Vickers hardnessparameters versus applied indentation test loads) to determine the role of vanadium particles on the general mechanicalcharacteristics with the aid of six mechanical modeling approaches, namely law of Meyer, proportional sample resistance,elastic/plastic deformation, modified proportional sample resistance, Hays-Kendall and indentation-induced cracking models.Throughout the study, the samples are prepared with the different molar rations varying from x=0 to 0.3 by the conventionalceramic method in the normal atmospheric pressure at the room temperature conditions. All the model findings show that themechanical performances tend to constantly reduce with increasing the vanadium concentration level embedded in the Bi-2223superconducting crystal system. This is in accordance to the fact that the concentration level of vanadium remarkably damages themain structural problems and permanent irreversible deformations. In this respect, it is not wrong to verify that the vanadiuminclusions unstabilize the inherit durable tetragonal phase of Bi-2223 inorganic solids, resulting in the regression in themechanical durability (resistance towards to the applied loads) in case of the applied test loads. Moreover, the modelsindicate that every material prepared exhibits the conventional indentation size effect (related to the formation of elastic andplastic deformations in the host crystal structures simultaneously due to the recovery of systems) but within the suppressiontrend. Shortly, all the semi-empiric models preferred in the present work are found to be useful descriptors to define thesuitable relationship between the ion-addition mechanism in the crystal lattice and mechanical durability/performances ofvanadium-added Bi-2223 materials. We should, of course, declare here that Hays–Kendall approach is gathered to be the best approach model for the load-independent Vickers hardness values in the plateau limit regions.
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    Experimental and theoretical approaches for structural and mechanical propertiesof novel side chain LCP-PP graft coproducts
    (2016) Çetin, Sedat; Şen, Behiye Öztürk; Soykan, Uğur; Firat, Elif Esra; Yildirim, Gürcan
    The monomers p-biphenyloxycarbonylphenyl acrylate (BPCPA) and p-biphenyloxycarbonylphenyl methacry-late (BPCPMA) were synthesized by the reaction of p-acryloyloxybenzoyl chloride and p-methacryloyloxybenzoyl chloridewith 4-hydroxybiphenyl, respectively, and polymerized by bulk polymerization in vacuum by using dicumyl peroxide.The graft copolymerization of the monomers onto polypropylene were carried out by bulk melt polymerization at 170◦Cwith various concentration levels of the monomers and the initiator in reaction mixtures. The content of monomers intheir graft coproducts increased with monomer-initiator percentage in the reaction medium. The graft coproducts werecharacterized by several available experimental techniques including differential scanning calorimetry, thermogravimetricanalysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and mechanical testing. Moreover, thecrucial changes in the mechanical performances pertaining to the polypropylene product were investigated by theoreticalcomputations performed based on the density functional theory (B3LYP) with the standard 6-311++G(d,p) level oftheory. According to obtained results, the mechanical properties of the graft coproducts deteriorated signi cantly withthe grafting of the homopolymers due to the damage of the rate-dependent viscoelastic deformation or yielding, leadingto enhancement in the surface energy values. At the same time, experimental evidence con rmed that the poly(BPCPA)materials exhibited much weaker secondary Van der Waals bonds than those in the poly(BPCPMA) products.
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    A VALUABLE VIEW ON EVALUATION OF GENERAL MECHANICAL PERFORMANCES PERTAINING TO Bi-2223 SUPERCONDUCTING CERAMICS WITH VANADIUM ADDITION
    (2020) Soykan, Uğur; Veliyeva, Fidan; Yildirim, Gürcan
    In this research, our scientific group investigates the effect of vanadium addition in the Bi-2223 superconducting matrix onthe general mechanical performance features by the help of experimental microhardness measurements conducted by a smallindenter between the well-defined stress loads of 0.245 N and 2.940 N. Moreover, we determine the key mechanical designparameters including the elastic moduli with the hardness, stiffness coefficients, fracture toughness, yield strength, brittlenessindex and its opposite behavior (ductility) in the applied test loads given using the experimental data deduced from themicroindentation tests. According to the experimental findings, it is oberved that the presence of vanadium content in the Bi2223 crystal structure surpasses seriously the general mechanical performance and related parameters due to the degradation inthe quality of grain boundary couplings, crystal structure and basic structural quantities as a consequence of the increment in thestructural problems, permanent plastic deformations, crack-producing flaws and dislocations. In other words, the augmentationof vanadium compounds in the Bi-2223 superconducting lattice brings about the considerable enlargement in the responsibilityto the static indentation loads. Namely, the sensitive level to the applied loads increases rapidly with the vanadium concentration.We also search the variation of graphs between the Vickers hardness parameters and applied test loads. In this respect, all thematerials prepared in this work exhibit the standard ISE (indentation size effect) characteristics but within the decrement trendas the vanadium content level increases. In more detail, the impurity atoms damage harshly the ISE feature of Bi-2223 type-IIsuperconducting ceramics. Additionally, we discuss the change of plateau limit regions coincided with the permeant artificialstructural problems in the graphics. The vanadium leads to shorten the applied test load values for the plateau limit regions ofBi-2223 materials, stemmed from the enhancement the general structural problems. To conclude, the vanadium inclusions areploughed to improve the general mechanical performance features and key mechanical design parameters.