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Hasan Kotan,Kris A. Darling,Tom Luckenbaugh 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
The key requirement to consolidate high-energy mechanically alloyed nanocrystalline powders is to achieve densificationand particle bonding without impairment in the mechanical properties. Recent demonstrations of consolidation methodsinvolving high shear, pressure and temperature have shown promising results for bonding high strength particulate materialsproduced by mechanical alloying. In this study, we report the ability of multi-pass high temperature equal channel angularextrusion to produce bulk ferritic alloys from nanocrystalline Fe–Ni–Zr powders. Subsequent microstructural characterizationsindicate limited grain growth as the average grain sizes remain smaller than 100 nm after processing temperatures of600 °C and 700 °C, above which grains reach micron sizes. The compression test results reveal that the alloys exhibit highmechanical strength at room and moderately high temperatures compared to the pure Fe and Fe–Ni alloys without Zr addition.
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Gökhan Polat,Hasan Kotan 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10
Stainless steels with Fe/Cr/Ni ratios of 74/18/8, 71/17/12, and 55/20/25 were produced from elemental powders by highenergy mechanical alloying at both room and cryogenic temperatures. The effect of mechanical alloying temperature onmartensitic transformation, the reversion of deformation-induced martensite-to-austenite upon annealing, and the influenceof cooling rate on the thermal stability of reversed austenite upon cooling to room temperature were investigated in detailby in-situ and ex-situ X-ray diffraction (XRD) experiments, transmission electron microscopy (TEM) and Thermo-Calcsimulations. A relative comparison of stainless steels after room temperature mechanical alloying indicated that the lownickel-containing steel underwent an almost complete martensitic transformation. However, martensitic transformation bydeformation through mechanical alloying at room temperature would not be possible with increasing nickel contents butwas created partially at cryogenic temperature, the degree of which depended on the steel composition. The in-situ XRDstudies exhibited that the deformation-induced martensite completely transformed to austenite at elevated temperatures. Thecomplete reverse transformation temperature simulated by Thermo-Calc software was found to be lower than that of theexperimentally determined ones. Additionally, the different cooling rates from the reversed austenite demonstrated that theslower cooling increased the thermal stability of reversed austenite at room temperature.
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Finite element study on composite slab-beam systems under various fire exposures
Burak K. Cirpici,Suleyman N. Orhan,Turkay Kotan 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.5
This paper presents an investigation of the thermal performance of composite floor slabs with profiled steel decking exposed to fire effects from floor. A detailed finite-element model has been developed by representing the concrete slab with steel decking under of it and steel beam both steel parts protected by intumescent coating. Although this type of floor systems offers a better fire resistance, passive fire protection materials should be applied when a higher fire resistance is desired. Moreover, fire exposed side is so crucial for composite slab systems as the total fire behaviour of the floor system changes dramatically. When the fire attack from steel parts, the temperature rises rapidly resulting in a sudden decrease on the strength of the beam and decking. Herein this paper, the fire attack side is assumed from the face of the concrete floor (top of the concrete assembly). Therefore, the heat is transferred through concrete to the steel decking and reaching finally to the steel beam both protected by intumescent coating. In this work, the numerical model has been established to predict the heat transfer performance including material properties such as thermal conductivity, specific heat and dry film thickness of intumescent coating. The developed numerical model has been divided into different layers to understand the sensitivity of steel temperature to the number of layers of intumescent coating. Results show that the protected composite floors offer a higher fire resistance as the temperature of the steel section remains below 60℃ even after 60-minute Standard (ISO) fire and Fast fire exposure. Obtaining lower temperatures in steel due to the great fire performance of the concrete itself results in lesser reductions of strength and stiffness hence, lesser deflections.
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Mehmet Dumlu Aydin,Ednan Bayram,Zekai Halici,Nazan Aydin,Canan Atalay,Hlzlr Ulvi,Dilcan Kotan,Cemal Gundogdu 대한약학회 2009 Archives of Pharmacal Research Vol.32 No.11
Nifedipine is a therapeutic drug in acute attacks of hypertension because of its rapid absorption from oral mucosa. Taste receptors are innervated by glossopharyngeal nerves (GPN) as well as by facial and vagal nerves. Sensory neurons of the GPNs are localised in the petrous ganglion (PG). Transection of the taste sensitive GPN fibres causes taste bud and PG degeneration and spontaneous hypertension. In this study, the role of chemical stimulation of the taste buds of the GPN by nifedipine and its role in treatment of hypertension were investigated in rabbits. Nifedipine was dropped sublingually (20 mg) for 4 days in the study group, followed by measuring blood pressures again. Then, the lingual branches of GPNs were cut. One month later, blood pressures were measured for 4 days. All animals were sacrificed humanely at the end of the experiment, and normal and degenerated neuron densities in the petrosal ganglions were enumerated stereologically. The antihypertensive effect of nifedipine decreased after GPNs denervation, in accordance with the increase of degenerated neurons in the PG. The chemical stimulation of taste buds of the GPNs by nifedipine may be an important effect of nifedipine application in addition to its calcium channel blocking effect. The rapid decrease in blood pressure following sublingual use of nifedipine may also result from the direct stimulation of taste buds innervated by the GPNs.
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