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      • KCI등재

        ON THE BOUNDS FOR THE SPECTRAL NORMS OF GEOMETRIC AND R-CIRCULANT MATRICES WITH BI-PERIODIC JACOBSTHAL NUMBERS

        UYGUN, SUKRAN,AYTAR, HULYA The Korean Society for Computational and Applied M 2020 Journal of applied mathematics & informatics Vol.38 No.1

        The study is about the bounds of the spectral norms of r-circulant and geometric circulant matrices with the sequences called biperiodic Jacobsthal numbers. Then we give bounds for the spectral norms of Kronecker and Hadamard products of these r-circulant matrices and geometric circulant matrices. The eigenvalues and determinant of r-circulant matrices with the bi-periodic Jacobsthal numbers are obtained.

      • KCI등재

        ON THE BOUNDS FOR THE SPECTRAL NORMS OF GEOMETRIC AND R-CIRCULANT MATRICES WITH BI-PERIODIC JACOBSTHAL NUMBERS

        Sukran Uygun,Hulya Aytar 한국전산응용수학회 2020 Journal of applied mathematics & informatics Vol.38 No.1

        The study is about the bounds of the spectral norms of r-circulant and geometric circulant matrices with the sequences called biperiodic Jacobsthal numbers. Then we give bounds for the spectral norms of Kronecker and Hadamard products of these r-circulant matrices and geometric circulant matrices. The eigenvalues and determinant of r-circulant matrices with the bi-periodic Jacobsthal numbers are obtained.

      • SCOPUSSCIEKCI등재

        Usefulness of End-to-Side Bridging Anastomosis of Sural Nerve to Tibial Nerve : An Experimental Research

        Civi, Soner,Durdag, Emre,Aytar, Murat Hamit,Kardes, Ozgur,Kaymaz, Figen,Aykol, Sukru The Korean Neurosurgical Society 2017 Journal of Korean neurosurgical society Vol.60 No.4

        Objective : Repair of sensorial nerve defect is an important issue on peripheric nerve surgery. The aim of the present study was to determine the effects of sensory-motor nerve bridging on the denervated dermatomal area, in rats with sensory nerve defects, using a neural cell adhesion molecule (NCAM). Methods : We compared the efficacy of end-to-side (ETS) coaptation of the tibial nerve for sural nerve defect repair, in 32 Sprague-Dawley rats. Rats were assigned to 1 of 4 groups : group A was the sham operated group, group B rats had sural nerves sectioned and buried in neighboring muscles, group C experienced nerve sectioning and end-to-end (ETE) anastomosis, and group D had sural nerves sectioned and ETS anastomosis was performed using atibial nerve bridge. Neurological evaluation included the skin pinch test and histological evaluation was performed by assessing NCAM expression in nerve terminals. Results : Rats in the denervated group yielded negative results for the skin pinch tests, while animals in the surgical intervention groups (group C and D) demonstrated positive results. As predicted, there were no positively stained skin specimens in the denervated group (group B); however, the surgery groups demonstrated significant staining. NCAM expression was also significantly higher in the surgery groups. However, the mean NCAM values were not significantly different between group C and group D. Conclusion : Previous research indicates that ETE nerve repair is the gold standard for peripheral nerve defect repair. However, ETS repair is an effective alternative method in cases of sensorial nerve defect when ETE repair is not possible.

      • KCI등재

        Mono/multinuclear cobaloxime and organocobaloxime-catalyzed conversion of CO2 and epoxides to cyclic organic carbonates: Synthesis and characterization

        Ahmet Kilic,Mahmut Ulusoy,Emine Aytar,Mustafa Durgun 한국공업화학회 2015 Journal of Industrial and Engineering Chemistry Vol.24 No.-

        The synthesis and characterization of the mono- and multinuclear cobaloxime and organocobaloxime complexes bearing bidentate dimethyl glyoxime ligands are presented. All mono- and multinuclear cobaloxime and organocobaloxime complexes are used as catalysts for the cycloaddition of CO2 to various epoxides, especially epichlorohydrin, in the presence of 4-dimethylamino pyridine (DMAP) as a cocatalyst. In the catalytic applications, DMAP was a more active base with higher yield compared to other Lewis bases. Complexes (1) and (3), which have two dimethyl glyoxime per cobalt center (mononuclear complexes), are better catalytic systems than the corresponding multinuclear cobaloxime and organocobaloxime complexes (2–5) and (7–10) with two dimethyl glyoxime per cobalt center and one linked ligands per copper center. In addition, the organocobaloxime complex (6) showed the highest activity for the cycloaddition of CO2 with epichlorohydrin in the presence of 4-dimethylamino pyridine (DMAP) as cocatalyst. The used as catalysts mono- and multinuclear cobaloxime and organocobaloxime complexes were characterized by 1H and 13C NMR spectra, FT-IR spectra, UV–vis spectra, LC-MS spectra, molar conductivity measurements, melting point measurements and magnetic susceptibility measurements.

      • KCI등재후보

        Concomitant Double Tumors of Myxopapillary Ependymoma Presented at Cauda Equina-Filum Terminale in Adult Patient

        Ulaş Yener,Mustafa Güdük,Murat Şakir Ekşi,Murat Hamit Aytar,Aydın Sav,Serdar Özgen 대한척추신경외과학회 2016 Neurospine Vol.13 No.1

        A 32-year-old man presented with gradually increasing bilateral buttock pain. He had intermittent claudication. Multiple, homogenously enhanced intradural extramedullary lesions at L2-L3 and L5-S1 levels were observed on magnetic resonance imaging. The tumors were debulked and were removed in piecemeal pattern until they had completely been resected. Histopathological examination of the surgical specimens confirmed that both tumors were myxopapillary ependymomas (MPE). MPE presenting as concomitant double tumor at conus-cauda-filum level are very rare. This kind of presentation could not be directly considered as dissemination, since both tumors were in the site of classical origin of MPE. Ten cases of double spinal MPEs have been reported to date. Including the present case, analysis of the 11 patients revealed some facts. There is a male predominance, which is opposite to the ependymomas that are commonly observed in females. Median age at presentation is 15 years. Most pronounced symptom is low back pain that sometimes radiates to lower extremities. Surgical approach was aimed in all tumors, which could be succeeded in all tumors except one. Adjuvant radiation therapy was applied in 5 patients. No recurrences have been reported after surgery or surgery + radiotherapy regimens.

      • KCI등재

        The Effect of Boronizing on the Magnetization Behaviour of Low Carbon Microalloyed Steels

        Adnan Calik,Mustafa Serdar Karaka?,Nazim Ucar,Omer Bari? Aytar 한국자기학회 2012 Journal of Magnetics Vol.17 No.2

        The change of saturation magnetization in boronized low carbon microalloyed steels was investigated as a function of boronizing time. Specimens were boronized in an electrical resistance furnace for times ranging from 3 to 9 h at 1123 K. The metallurgical and magnetic properties of the specimens were investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). A boride layer with saw-tooth morphology consisting of FeB and Fe₂B was observed on the surface, its thickness ranged from 63 ㎛ to 140 ㎛ depending on the boronizing time. XRD confirmed the presence of Fe₂B and FeB on the surface. The saturation magnetization decreased with increasing boronizing time. This decrease was attributed to the increased thickness of the FeB and Fe₂B phases. Cracks were observed at the FeB/Fe₂B interfaces of the samples. The number of interfacial cracks increased with increasing boronizing time.

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