Plastic / Superplastic Forming : STRAIN RATES EFFECT ON THE THICKNESS DISTRIBUTION OF SUPERPLASTICALLY DEFORMED Ti - ALLOY PIPE INTO SPHERICAL SHAPE

Nihat Akkus,Masanori Kawahara,Hisashi Nishimura 대한금속재료학회 ( 구 대한금속학회 ) 1995 Advanced Material and Processing Vol.1 No.-

Effects on Anabolic Androgenic Steroids Muscle and Skeleton System Used by Taekwondo Athletes

( Hasan Akkus ),( Metin Sahin ),( Ali Sagirkaya ),( Sefa Lok ) 국제태권도학회 2017 International Symposium for Taekwondo Studies Vol.2017 No.-

Anabolic androgenic steroids (AAS) are synthetic derivatives of testosterone. Testosterone and AAS are used clinically for the treatment of renal failure, anemia, growing deficiency in children, delayed puberty, and in case of some chronic weakness such as AIDS and cancer. According to surveys and media reports, the illegal use of these drugs to increase muscle size and strength is widespread. There is a growing body of evidence that AAS have positive anabolic actions on the musculoskeletal system, influencing lean body mass, muscle size, strength, protein metabolism, bone metabolism, and collagen synthesis. Skeletal muscle is a primary target tissue for the anabolic effects of AAS. Supraphysiological doses of testosterone administered to healthy young men over periods lasting 10-20 wk increase lean body mass, muscle size, and strength with or without exercise. The anabolic effect of testosterone is dose dependent, and significant increases in muscle size and strength only occur with doses of 300 mg and higher. The testosterone-induced increase in muscle size and strength is due to a dose-dependent hypertrophy that results from an increase in cross-sectional area of muscle fibers and an increase in myonuclear number. Evidence suggests that these morphometric effects are the result of a testosterone-induced increase in muscle protein synthesis. AAS also enhance collagen synthesis and increase bone mineral density. The anabolic effect of AAS is mediated primarily by androgen receptors in skeletal muscle. Testosterone has potent anabolic effects on the musculoskeletal system, including an increase in lean body mass, a dose-related hypertrophy of muscle fibers, and an increase in muscle strength. For Taekwondo athletes requiring speed and strength and men desiring a cosmetic muscle makeover, illegal steroids are a powerful lure, despite the risk of subjective side effects.

The investigation of wear properties of different hard filling welding electrodes used in repair welding

Ahmet Akkus 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.10

The surface of tamping machıne's digger is covered with a filler material because it is a material that is continuously used in TCDD (The State Railways of the Turkish Republic) lines and it is a material that needs to be constantly changed because it is exposed to abrasion. For many years, this process with the same method and same electrodes. In our work, we aimed to produce a variety of welding electrodes with a more efficient, longer-lasting and less labor-intensive method for production tamping machine’s digger. Considering factors such as applicability, easy availability, cost, welding method and hard facing welding electrodes to be used in our work have been determined. The necessary materials were then provided. The diggers of tamping machines were welded with 5 different welding electrodes. Then, the effect of each of these electrodes on the mechanical properties and strength was compared. Used tamping machine’s diggers processing was carried out with different hardfacing welding electrodes. Mechanical properties and strength effects of different welding electrodes was analyzed.

Fabrication and characterization of aluminium titanate and mullite added Porcelain ceramics

Ahmet Akkus,Tahsin Boyraz 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.1

In this study, aluminium titanate (AT, Al2TiO5) and mullite (M, 3Al2O3·2SiO2) ceramics were synthesized by reaction sinteringfrom Al2O3, SiO2 and TiO2 powders which consisted of homogenization by wet ball milling followed by sintering AT and Min air at 1550 oC for 2 hrs and 1400 oC for 2 hrs, respectively. AT and M in different amounts (0 and 20 wt. %) were mixedwith Porcelain (P). AT and M reinforced porcelain ceramics were prepared by the powder metallurgy route. After drying, thepowders were compressed to preforms of 56x12x10 mm by uniaxial pressing at 200 MPa. The green compacts were sinteredat 1100-1200 oC for 1-5 hr under air. Investigations were carried out, on the effect of addition of AT and M in terms of physicalproperties, microstructure, XRD phases, as well as wear and mechanical properties of AT and M-reinforced porcelain ceramiccomposites. Phase and microstructural characterizations of the sintered materials were carried out by using X-ray diffractiontechnique (XRD) and scanning electron microscope (SEM). The Micro Vickers hardness testing was performed using theShimadzu HMV-MIII hardness tester.

Experimental research and use of finite elements method on mechanical behaviors of honeycomb structures assembled with epoxy-based adhesives reinforced with nanoparticles

Harun Akkus,Hayrettin Duzcukoglu,Omer Sinan Sahin 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1

This study utilized experimental and finite element methods to investigate the mechanical behavior of aluminum honeycomb structures under compression. Aluminum honeycomb composite structures were subjected to pressing experiments according to the standard ASTM C365. Resistive forces in response to compression and maximum compressive force values were measured. Structural damage was observed. In the honeycomb structure, the cell width decreased as the compressive force increased. Results obtained with finite element models generated using ANSYS Workbench 15 were validated. Experimental results paralleled the finite element modeling results. The ANSYS results were approximately 85 % reliable.

Investigation of wear properties of CaO, MgO added stabilized zirconia ceramics produced by different pressing methods

Ahmet Akkus,Tahsin Boyraz 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.3

Stabilized zirconia has superior high temperature properties such as high tolerance for thermal shock, low thermalconductivity, mechanical properties, elevated melting point, good phase stability and excellent oxidation resisNtance. Thepresent paper describes the fabrication and wear behaviour of 8 mole% CaO, 4 mole % CaO-4 mole% MgO and 8 mole%MgO - stabilized zirconia (ZrO2) based composites fabricated by the conventional ceramic production process. CaO/MgOadded stabilized zirconia ceramics were fabricated by using a combined method of ball milling, cold press-cold isostaticpressing and sintering. The powder blends containing different amounts of % 8 mole CaO/MgO were wet-milled for 1 hr ina vibratory ball-mill using zirconia vial and balls. After drying, powders were compacted to cylindrical preforms with adiameter of 12.7 mm by uniaxial pressing at 300 MPa and by cold isostatic pressing at 300 MPa. The green compacts weresintered at 1600 oC for 3 hrs under air. Phase and microstructural characterizations of the sintered materials were carried outby using X-ray diffraction technique (XRD) and scanning electron microscope (SEM). The Micro Vickers hardness testing wasperformed using the Shimadzu HMV-MIII hardness tester. Plint brand abrasion tester was used for the abrasion tests ofceramics. As a result, it has been observed that the hardness is increased by increasing the amount of MgO and the ceramicsproduced by cold isostatic pressing are harder.

Electronic and Optical Properties of γ-Ag3SI by Using First Principles

Bahattin Erdinc,Harun Akkus 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3

The electronic energy band structure and the optical properties of γ-Ag3SI are calculated by using density functional theory under the local density approximation (LDA). The calculated electronic band structure shows that γ-Ag3SI has an indirect gap with a value of 0.46 eV at the M →Γpoints in the Brillouin zone. A structural optimization has been performed by using the LDA. The optical spectra of the γ-Ag3SI in the photon range up to 30 eV are calculated by using a first-principles method under the scissor approximation. The real and the imaginary parts of the dielectric function as functions of the photon energy and, thus, the optical constants, such as the energy-loss function, the refractive index, and the effective number of electrons, are investigated. The calculated structural optimization of γ-Ag3SI is compared with the experimental results and is found to be in good agreement with the experimental data.

Investigation of wear properties of mullite and aluminium titanate added porcelain ceramics

T. Boyraz,A. Akkus 한양대학교 세라믹연구소 2021 Journal of Ceramic Processing Research Vol.22 No.2

In this study, the effects of aluminium titanate and mullite added porcelain ceramic composites produced by the traditionalceramic production process on the wear behaviour of the applied load and time were investigated. Aluminium Titanate(Al2TiO5) and Mullite (3Al2O3.2SiO2) ceramics were synthesized by reaction sintering from Al2O3, SiO2 and TiO2 powdersconsisting of homogenization by wet ball milling followed by sintering Al2TiO5 (AT) and 3Al2O3.2SiO2 (M) in atmosphereconditions at 1,550 oC for 2 h and 1,400 oC for 2 h, respectively. AT and M in amounts of 0 and 20 wt.% were mixed withPorcelain (P). AT and M reinforced porcelain ceramics were prepared by the powder metallurgy route. After drying, thepowders were compressed to preforms of 56 × 12 × 10 mm by uniaxial pressing at 200 MPa. The green compacts were sinteredat 1100-1200 oC for 1-5 h in air. Investigations were carried out, on the effect of addition of Al2TiO5 and 3Al2O3.2SiO2 in termsof physical properties, microstructure, XRD phases, as well as wear and mechanical properties of 3Al2O3.2SiO2 and Al2TiO5-reinforced porcelain ceramic composites. Phase and microstructural characterizations of the sintered materials were carriedout by using X-ray diffraction technique (XRD) and scanning electron microscope (SEM). The Micro Vickers hardness testingwas performed using the Shimadzu HMV-MIII hardness tester. PLINT brand abrasion tester was used for the abrasion testsof ceramics. As a result, as the load and time increased in all samples, the amount of wear increased. While the wear volumein the P sample under 70 N load for 5 min was 5.15 × 10−2 mm3, it reached 33.33 × 10−2 mm3 in 20 min under 120 N load. Similarly, these values were measured as 0,66 × 10−2 mm3 and 5.48 × 10−2 mm3 in the PAT sample, 1.09 × 10−2 mm3 and7.41 × 10−2 mm3 in the PM sample and 1.75 × 10−2 mm3 and 38.44 × 10−2 mm3 in the PMAT sample. M and AT additivesimprove the wear properties of porcelain, while M and AT both have negative effects on wear.

In Vitro Antimicrobial, Antioxidant, and Antispasmodic Activities and the Composition of the Essential Oil of Origanum acutidens (Hand.-Mazz.) Ietswaart

Ismihan Goze,Ahmet Alim,Senay Akkus Cetinus,Ali Cetin,Nedim Durmus,Ahmet Turan Atas,Nilufer Vural 한국식품영양과학회 2010 Journal of medicinal food Vol.13 No.3

The radical scavenging, antimicrobial, and antispasmodic activities and the composition of Origanum acutidens (Hand.-Mazz.) Ietswaart (Order Labiatte) essential oil were evaluated in vitro. Gas chromatography/mass spectrometry analysis of the oil resulted in the identification of 20 compounds, representing 93.61% of the oil; carvacrol (65%) was the main component. The sample was also subjected to a screening for antioxidant activity by using the 1,1-diphenyl-2-picrylhydrazyl and β-carotene/linoleic acid assays. The essential oil exhibited strong antioxidant activity. Using the agar disk diffusion method, antimicrobial activities of the essential oils were determined for nine microorganisms; antimicrobial activity was shown against eight of them. O. acutidens oil exhibited spontaneous contractions in rat ileum at the 100% level at 0.1mg/mL level.

New Representations of Pascal Matrix via Operational $q$-calculus

Gonca Kizilaslan,De-Yin Zheng,Ilker Akkus 호남수학회 2022 호남수학학술지 Vol.44 No.1

In this paper we introduce two type of representations of the Pascal matrix via induced transformations of some $q$-derivatives as well as their some combinatorial applications.