Yazar "Koc, A" seçeneğine göre listele
Listeleniyor 1 - 6 / 6
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe 3-D analysis of temperature distribution in the material during pulsed laser and material interaction(Springer, 2004) Koc, ARecently, lasers are being increasingly used in the industry owing to their precision and low cost. Material is heated and evaporated during laser and material interaction due to the absorption of laser beams by the material. In this study, a 3-D Laser heating model including evaporation has been solved using the electron- kinetic theory approach. The basis in examining the problem using the kinetic theory approach is to describe the heat conduction through electron-phonon and molecule-phonon collisions. The problem is solved by using the electron-kinetic theory approach in such a way that heat conduction is taken into account until the material is heated to its melting temperature and non-conduction limited heat transfer is considered after the melting temperature is reached. Non-conduction limited heat transfer through the phase change process is resulted from vacancy-molecule collisions. A numerical scheme is introduced to solve the governing equation, owing to the fact that the energy equation resulted is in the form of integro-differential equation. Four different materials, namely iron, nickel, tantalum and titanium are chosen in this study determine the material response to laser pulse heating. For each material, time dependent temperature distribution through the depth of the material and on the surface of the material is computed and analyzed for four different materials.Öğe Design and analysis of a water-ammonia absorption refrigeration system(Professional Engineering Publishing Ltd, 2000) Koc, A; Bulgan, AT; Öztürk, NAA water-ammonia absorption refrigeration (AAR) system is preferred to classical vapour compression when a heat source is available cheaply. This study deals with the analysis of an AAR system operating with a low-temperature heat source. Eleven design variables were chosen for this purpose. The analysis showed that the use of a low temperature heat source imposes some restrictions on the system design, but an economically operating AAR system may be designed by a careful process optimization study.Öğe Investigation of thermodynamic properties of alternative fluid couples for absorption thermal systems(Pergamon-Elsevier Science Ltd, 2000) Bulgan, AT; Koc, A; Öztürk, NAOne of the reasons for depletion of the ozone layer of the atmosphere is the use of materials in different industrial brands which have disintegrating effects on ozone in their compositions. It is known that thermodynamic analysis of the operating processes of machines and systems that use heat energy depends on calculations of the heat transfer processes of parts of the system and choices of the thermohydrodynamic regimes and parameters. In this study, an experimental investigation is conducted on the thermal properties which are close to the curves of liquid and two phase boiling and condensing of two new fluid couples for absorption cooling systems, and absorption heat pumps which are better ecologically. The obtained results are analyzed, and new equations are given. Experiments are done for methanol-LiBr and methanol-LiCl solutions with changes of pressure, changes of temperature and concentrations of solutions in the ranges of 0.1-40 MPa, 298-498 K, 2-12%, respectively. During the experiments, extreme care is taken to keep the solution concentration stable, and the obtained results are analyzed in different thermodynamical coordinates. State equations are constructed according to the values of specific volume, and the main thermodynamical properties are calculated with the use of the differential equations of thermodynamics. Values related with these calculations are given in tables. (C) 2000 Elsevier Science Ltd. All rights reserved.Öğe Protective agent, erdosteine, against cisplatin-induced hepatic oxidant injury in rats(Springer, 2005) Koc, A; Duru, M; Ciralik, H; Akcan, R; Sogut, SCisplatin, one of the most active cytotoxic agents against cancer, has several toxicities. Hepatotoxicity is one of them occurred during high doses treatment. The aim of this study was to determine the effects of erdosteine against cisplatin-induced liver injury through tissue oxidant/antioxidant parameters and light microscopic evaluation. The rats were randomly divided into three groups: control (n=5), cisplatin (10 mg/kg, n=6) and cisplatin+erdosteine (50 mg/kg/day oral erdosteine, n=8) groups. The rats were sacrificed at the 5th day of cisplatin treatment. The liver tissues were examined with light microscopy and oxidant/antioxidant biochemical parameters. The malondialdehyde (MDA) and nitric oxide (NO) levels were increased in the cisplatin group in comparison with the control and cisplatin+erdosteine groups (p < 0.05). There was no significant difference in MDA and NO levels between control and cisplatin+erdosteine groups. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) were higher in cisplatin+erdosteine group than cisplatin group (p < 0.05). However, the CAT and GSH-Px activities were significantly lower in cisplatin group than in control group (p < 0.05). The light microscopic examination revealed that cytoplasmic changes especially around cells of central vein were observed in cisplatin group. Hepatocellular vacuolization was seen in these cells. In the cisplatin plus erdosteine group, a decrease in cytoplasmic changes with the hepatocytes and sinusoidal dilatations around cells of central vein were noticed in as compared to cisplatin group. In the light of microscopic and biochemical results, it was concluded that cisplatin-induced liver damage in high dose and erdosteine prevented this toxic side effect by the way of its antioxidant and radical scavenging effects.Öğe The protective role of erdosteine on testicular tissue after testicular torsion and detorsion(Springer, 2005) Koc, A; Narci, A; Duru, M; Gergerlioglu, HS; Akaydin, Y; Sogut, STesticular torsion and detorsion are important clinical problems for infertile man and oxidative stress may have a role in this clinical situation. The aim of this study was to investigate the protective role of erdosteine, an antioxidant, on unilateral testicular reperfusion injury in rats. The rats were divided into four groups including seven rats in each group: control, torsion, torsion/detorsion and torsion/detorsion+erdosteine. Rats, except the sham operation group, were subjected to left unilateral torsion (720 degrees rotation in the clockwise direction) without including the epididymis. The experiments were finished after sham operation time for control, 120 min torsion for torsion group and 120 min torsion and 240 min detorsion for torsion/detorsion groups. Bilateral orchiectomy was performed for all groups of rats. The ipsilateral and controlateral testis were divided into two pieces to analyse biochemical parameters and to investigate the light microscopic view. Malondialdehyde level of ipsilateral testis was increased in torsion and torsion/detorsion groups in comparison with the other groups (p < 0.05). Erdosteine treatment ameliorated lipid peroxidation after torsion/detorsion in ipsilateral testis (p < 0.05). Also, xanthine oxidase activity of ipsilateral testis was increased in torsion/detorsion group in comparison with the others (p < 0.05). Nitric oxide (NO) level of ipsilateral testis was higher in all experimental groups than sham operated control group (p < 0.05). Also, NO level of torsion group was increased in comparison with detorsion groups (p < 0.05). Erdosteine treatment caused increased glutathione peroxidase activity in comparison with torsion and torsion/detorsion groups and catalase activity in comparison with the other groups in ipsilateral testis (p < 0.05). Superoxide dismutase activity of ipsilateral testis was higher in torsion/detorsion and torsion/detorsion+erdosteine groups than control and torsion groups (p < 0.05). The biochemical parameters were not affected in controlateral testis in all groups. Torsion, torsion/detorsion and torsion/detorsion+erdosteine groups showed ipsilateral testicular damage in the histological examination, but the specimens from torsion/detorsion had a significantly greater histological injury than those from the other groups (p < 0.05). Control rats showed normal seminiferous tubule morphology. Rats in torsion group had slight-to-moderate disruption of the seminiferous epithelium. Rats in torsion/detorsion group displayed moderate-to-severe disruption of the seminiferous epithelium. In all animals from torsion/detorsion+erdosteine group, the testicular tissues were affected with slight-to-moderate degenerative changes of the seminiferous epithelium. Administration of erdosteine resulted in a significantly reduced histological damage associated with torsion of the spermatic cord compared with torsion/detorsion. In all groups, the contralateral testes were histologically normal. In conclusion, the results clearly displayed that erdosteine treatment may have a protective role on testicular torsion/detorsion injury.Öğe The protective role of topical propolis on experimental keratitis via nitric oxide levels in rabbits(Springer, 2006) Duran, N; Koc, A; Oksuz, H; Tamer, C; Akaydin, Y; Kozlu, T; Çelik, MThe aim of this study was to investigate antioxidant, anti-inflammatory, and antibacterial properties of propolis in the treatment of experimental Staphylococcus aureus keratitis. Twenty young New Zealand white rabbits were used in this experiment. Staphylococcus aureus were given by intrastromal injection to 16 rabbits and 4 rabbits were used as control group (Group 1). Group 2 was treated with phosphate-buffered solution drops; Group 3 was administered ethanolic extract of propolis drops; Group 4 received topical ciprofloxacin drops; Group 5 was treated with topical ciprofloxacin drops along with ethanolic extract of propolis drops. The eyes were examined by slit lamp to assess corneal opacity. And then, corneas were removed to determine nitric oxide (NO) levels and count bacteria. Corneas were also evaluated histologically. Corneal NO concentration in gruop 5, treated with a combination of propolis and ciprofloxacin was determined significantly lower (10.0 +/- 1.8 mu mol/g wet tissue) than in Group 4, treated with ciprofloxacin (24.0 +/- 3.1 mu mol/g wet tissue), from Group 3, treated with propolis (15.6 +/- 1.8 mu mol/g wet tissue), and treated with PBS (44.7 +/- 7.8 mu mol/g wet tissue). There were significantly fewer bacteria in eyes that received propolis plus ciprofloxacin than in eyes treated with ciprofloxacin (p=0.0001) or propolis (p=0.0001) or eyes treated with PBS (p=0.0001). The light microscopic examination revealed that the control group showed normal corneal morphology. In the nontreated group, sections of the stromal infiltration revealed the presence of inflammatory cells, which were diffusely distributed (p < 0.05). Administrations of ciprofloxacin plus propolis resulted in a significantly reduced histological damage with fewer bacterial inoculation of the corneal stroma in comparison with the other groups (p < 0.05). Based on these findings, we suggest that ethanolic extract of propolis has antioxidant, anti-inflammatory, and antibacterial properties for S. aureus keratitis in rabbits.
