A robust numerical technique for solving non-linear Volterra integro-differential equations with boundary layer

Firat Cakir,Musa Cakir,Hayriye Guckir Cakir 대한수학회 2022 대한수학회논문집 Vol.37 No.3

In this paper, we study a first-order non-linear singularly perturbed Volterra integro-differential equation (SPVIDE). We discretize the problem by a uniform difference scheme on a Bakhvalov-Shishkin mesh. The scheme is constructed by the method of integral identities with exponential basis functions and integral terms are handled with interpolating quadrature rules with remainder terms. An effective quasi-linearization technique is employed for the algorithm. We establish the error estimates and demonstrate that the scheme on Bakhvalov-Shishkin mesh is $O(N^{-1})$ uniformly convergent, where $N$ is the mesh parameter. The numerical results on a couple of examples are also provided to confirm the theoretical analysis.

Anthropometric-Somatotype and Strength Profiles and On-Water Performance in Turkish Elite Kayakers

( Firat AKCA ),( Surhat Muniroglu ) 한국스포츠정책과학원(구 한국스포츠개발원) 2008 International Journal of Applied Sports Sciences Vol.20 No.1

The aim of this study was to investigate some physical and strength characteristics and relationships of these characteristics with performance of Turkish national flatwater kayak team male athletes. Eleven male Turkish national team paddlers, mean (SD) age 21,5 (2,16) years old, participated in this investigation. Testing was conducted over 5 days and included anthropometric, somatotype measurements and strength, running and flatwater kayak tests (200 m., 500 m., 1000 m.). Anthropometric assessments taken were the measurements of body mass, stature, the sum of four skinfolds and estimated percent body fat. Girth measurements and bone breadths were taken to allow the calculation of somatotype using the Heath-Carter procedure. Pearson product moment correlations were employed to determine the relationship of all parameters with flatwater kayak performance. The significant negative correlations were found between 500 m. and 1000 m. performance times and body weight (respectively; r=0.78, p<0.05 and r=0.71, p<0.05). The significant negative correlations were found between 1 RM bench row and 200 m. and 500 m. performance times (respectively; r=0.68, p<0.05 and r=0.80, p<0.01). Significant relationships with 200 m. time were found for the biceps and flexed biceps girth (respectively, r=-0.70, p<0.05, and r=-0.80, p<0.01). Significant relationships with 500 m. time were found for the biceps, flexed biceps and thigh girth (respectively; r=-0.76, p<0.01, r=-0.86, p<0.01, r=-0.81, p<0.01). Physical characteristics of Turkish national flatwater kayak team athletes were found similar when compared to international class flatwater kayakers from different countries except upper body dimensions. Because of the strong relationships between upper body dimensions and flatwater kayak performance; the training of Turkish flatwater kayakers should be more focused on improving upper body musculature and strength.

Effect of Heat Treatment Conditions and Densities on Residual Stresses at Hybrid (FLN2-4405) P/M Steels

Kafkas Firat,Karatas Cetin,Saritas Suleyman 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

The characteristics of residual stresses occurring in PM steel based nickel (FLN2-4405) was investigated. The measurements of residual stresses were carried out by electrochemical layer removal technique. The values and distributions of residual stresses occurring in PM steel processed under various densities and heat treatment conditions were determined. In most of the experiments, tensile residual stresses were recorded in surface of samples. The residual stress distribution on the surface of the PM steels is affected by the heat treatment conditions and density. Maximum values of residual stresses on the surface were observed sinter hardened condition and density. Minimum level of recorded tensile residual stresses are150 MPa and its maximum level is 370 MPa.

Omega-3 fatty acids inhibit oxidative stress in a rat model of liver regeneration

Ozgur Firat,Ozer Makay,Levent Yeniay,Goksel Gokce,Cigdem Yenisey,Ahmet Coker 대한외과학회 2017 Annals of Surgical Treatment and Research(ASRT) Vol.93 No.1

Purpose: Lipid peroxidation and consequent reactive oxygen species in the setting of oxidative stress have crucial roles in liver regeneration, which may adversely affect the regeneration itself and lead to liver failure. The aim of the current study is to investigate whether omega-3 fatty acid supplementation inhibits oxidative stress in an experimental model of liver regeneration. Methods: Forty rats were allocated to four groups. Rats in group A received a sham operation. Rats in group B were subjected to right portal vein ligation (RPVL) and saline infusion. Rats in groups C and D were subjected to RPVL and total parenteral nutrition (TPN) with an all-in-one admixture containing a soybean oil based lipid emulsion. Rats in group D were additionally supplemented with omega-3 fatty acid infusion. Oxidative stresses in the blood and liver were measured by glutathione, superoxide dismutase, catalase, glutathione peroxidase, malondialdehyde, and nitric oxide. Results: Omega-3 supplementation to the TPN solution significantly corrected alterations in the blood and tissue concentrations of oxidants and anti-oxidants during regeneration (P < 0.05). Conclusion: Omega-3 fatty acid supplementation to the TPN solution revealed promising results in removal of oxidative stress that emerges during liver regeneration.

ON THE GEOMETRY OF THE CROSSED PRODUCT OF GROUPS

Ates, Firat,Cevik, Ahmet Sinan,Karpuz, Eylem Guzel Korean Mathematical Society 2021 대한수학회보 Vol.58 No.5

In this paper, firstly, we work on the presentation of the crossed product of groups of general types. After that we find the generating pictures (Second Homotopy Group) of this product by looking the relations from a geometric viewpoint. Finally, we give some applications.

Effect of substitution of basalt for quartz in triaxial porcelain

Fatma A. Firat 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.6

Porcelain is a material produced from kaolinitic clay, quartz and feldspar. Recently, research on new materials such as nonhazardous wastes and natural rocks have been focused on replacing traditional constituents without changing the process or quality of the final products. The aim of this study is to investigate the possibility of the use of volcanic basalt rock in porcelain production. Quartz was progressively replaced by up to 20 wt.% basalt in a traditional porcelain composition. The samples were sintered in an electric furnace with a heating rate of 5 ο K minute-1 at 1100, 1150, 1200, 1250 and 1300 ο C for 2 h. The effects of this substitution were investigated by measuring the linear shrinkage, bulk density and apparent porosity. The sintered samples were also characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The effects of this substitution on sintering and microstructural properties are studied. According to the experimental results linear shrinkage and bulk density values were decreased and the apparent porosity ratios were increased by substitution of quartz by basalt. XRD analysis showed that there are three phases consisting of albite, quartz and mullite at the final basalt containing bodies and mullite peaks were increased by increasing the basalt content. SEM studies revealed that there were unresolved quartz, meta-kaolen and mullite in a glassy matrix.

Cyclic behavior of various sands and structural materials interfaces

Cabalar, Ali Firat Techno-Press 2016 Geomechanics & engineering Vol.10 No.1

This paper presents the results of an intensive experimental investigation on cyclic behavior of various sands and structural materials interface. Comprehensive measurements of the horizontal displacement and shear stresses developed during testing were performed using an automated constant normal load (CNL) cyclic direct shear test apparatus. Two different particle sizes (0.5 mm-0.25 mm and, 2.0 mm-1.0 mm) of sands having distinct shapes (rounded and angular) were tested in a cyclic direct shear testing apparatus at two vertical stress levels (${\sigma}=50kPa$, and 100 kPa) and two rates of displacement ($R_D=2.0mm/min$, and 0.025 mm/min) against various structural materials (i.e., steel, concrete, and wood). The cyclic direct shear tests performed during this investigation indicate that (i) the shear stresses developed during shearing highly depend on both the shape and size of sand grains; (ii) characteristics of the structural materials are closely related to interface response; and (iii) the rate of displacement is slightly effective on the results.

Outcome of the patients with chronic mesh infection following open inguinal hernia repair

Cihangir Akyol,Firat Kocaay,Erkinbek Orozakunov,Volkan Genc,Ilknur Kepenekci Bayram,Atil Cakmak,Semih Baskan,Ercument Kuterdem 대한외과학회 2013 Annals of Surgical Treatment and Research(ASRT) Vol.84 No.5

Purpose: Hernia repairs are the most common elective abdominal wall procedures performed by general surgeons. The use of a mesh has become the standard for hernia repair surgery. Herein, we discuss a management strategy for chronic mesh infections following open inguinal hernia repair with onlay prosthetic mesh. Methods: In this study, 15 patients with chronic mesh infections following open inguinal hernia repairs were included. The medical records of these patients were retrospectively reviewed and information regarding presentation, type of previous hernia repair, type of mesh, operative findings and bacteriological examination results were obtained. In all cases, the infected mesh was removed completely and the patients were treated with antibiotic regimens and local wound care. Results: Fifteen mesh removals due to chronic infection were performed between January 2000 and March 2012. The mean interval of hernia repair to mesh removal was 49 months. All patients were followed up for a median period of 62 months (range, 16 to 115 months). In all patients, the infections were resolved successfully and none were persistent or recurrent. However, one patient developed recurrent hernia and one developed nerve injury. Conclusion: Chronic mesh infection following hernia repair mandates removal of the infected mesh, which rarely results in hernia recurrence.

A comparison of the performance characteristics of large 2 MW and 3 MW wind turbines on existing onshore wind farms

Mehmet Bilgili,Firat Ekinci,Tugce Demirdelen 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.32 No.2

The aim of the current study is to compare the performance of large 2 MW and 3 MW wind turbines operating on existing onshore wind farms using Blade Element Momentum (BEM) theory and Angular Momentum (AM) theory and illustrate the performance characteristic curves of the turbines as a function of wind speed (U∞). To achieve this, the measurement data obtained from two different Wind Energy Power Plants (WEPPs) located in the Hatay region of Turkey was used. Two different horizontal-axis wind turbines with capacities of 2 MW and 3 MW were selected for evaluation and comparison. The hub-height wind speed (UD), turbine power output (P), atmospheric air temperature (Tatm) and turbine rotational speed (Ω) data were used in the evaluation of the turbine performance characteristics. Curves of turbine power output (P), axial flow induction factor (a), turbine rotational speed (Ω), turbine power coefficient (CP), blade tip speed ratio (λ), thrust force coefficient (CT) and thrust force (T) as a function of U∞ were obtained for the 2 MW and 3 MW wind turbines and these characteristic curves were compared. Results revealed that, for the same wind speed conditions, the higher-capacity wind turbine (3 MW) was operating at higher turbine power coefficient rates, while rotating at lower rotational speed ratios than the lower-capacity wind turbine (2 MW).

Lateral Locked Plating or Dual Plating: A Comparison of Two Methods in Simple Bicondylar Tibial Plateau Fractures

Caner Citak,Cemil Kayali,Firat Ozan,Taskin Altay,Huseyin Gokhan Karahan,Kamil Yamak 대한정형외과학회 2019 Clinics in Orthopedic Surgery Vol.11 No.2

Background: In this study, our aim was to compare the results of the dual locking plate fixation technique and lateral locking plate fixation technique for tibial bicondylar plateau fractures without posteromedial fragment. Methods: We evaluated 20 patients who underwent surgical treatment due to bicondylar tibial plateau fracture between 2010 and 2015. Ten patients were included in group 1, in which a dual locking plate was employed, whereas 10 patients were included in group 2, in which a lateral locking plate was used. In both groups, functional and clinical outcomes after treatment were rated according to the Knee Society Knee Scoring System, Rasmussen functional score, and Rasmussen radiological score. Results: The mean follow-up time was 24 months. There were no significant differences between the groups with respect to functional and radiographic outcomes at the final follow-up. Conclusions: In bicondylar tibial plateau fractures without posteromedial fragment, the lateral locking plate fixation technique showed the similar clinical and radiological outcomes as the dual locking plate fixation technique.