Structural repairing of damaged reinforced concrete beam-column assemblies with CFRPs

Yurdakul, Ozgur,Avsar, Ozgur Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.3

Depending on the damage type as well as the level of damage observed after the earthquake, certain measures should be taken for the damaged buildings. In this study, structural repairing of two different types of damaged RC beam-column assembly by carbon fiber-reinforced polymer sheets is investigated in detail as a member repairing technique. Two types of 1:1 scale test specimens, which represent the exterior RC beam-column connection taken from inflection points of the frame, are utilized. The first specimen is designed according to the current Turkish Earthquake Code, whereas the second one represents a deficient RC beam-column assembly. Both of the specimens were subjected to cyclic quasistatic loading in the laboratory and different levels of structural damage were observed. The first specimen displayed a ductile response with the damage concentrated in the beam. However, in the second specimen, the beam-column joint was severely damaged while the rest of the members did not attain their capacities. Depending on the damage type of the specimens, the damaged members were repaired by CFRP wrapping with different configurations. After testing the repaired specimens, it is found that former capacities of the damaged members were mostly recovered by the application of CFRPs on the damaged members.

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.

A Flight Data Visualization Framework

Ozgur Aydin Yuksel,Jae Sug Ki 한국HCI학회 2003 한국HCI학회 학술대회 Vol.2003 No.2

A Flight Data Visualization Framework

Ozgur Aydin Yuksel,Jae Sug Ki 한국정보과학회 2003 한국정보과학회 학술발표논문집 Vol.2003 No.2

Chemical composition and anti-biofilm activity of Thymus sipyleus BOISS. subsp. sipyleus BOISS. var. davisianus RONNIGER essential oil

Ozgur Ceylan,Aysel Ugur 대한약학회 2015 Archives of Pharmacal Research Vol.38 No.6

In this study, antimicrobial and antibiofilmactivities and the chemical composition of Thymus sipyleusBOISS. subsp. sipyleus BOISS. var. davisianus RONNIGERessential oil was evaluated. The essential oil wasobtained by hydro-distillation and analyzed by gas chromatography-mass spectrometry. Fourteen compounds werecharacterized, having as major components thymol(38.31 %) and carvacrol (37.95 %). Minimum inhibitoryconcentrations (MICs) of oil and the major componentswere calculated by serial dilution method, and anti-biofilmeffects by microplate biofilm assay against five Grampositive (Staphylococcus aureus MU 38, MU 40, MU 46,MU 47, Stahylococcus epidermidis MU 30) and five Gramnegative (Pseudomonas aeruginosa MU 187, MU 188, MU189, Pseudomonas fluorescens MU 180, MU 181) bacteria. It was found that MICs for essential oil, thymol and carvacrolwere between 5 and 50 ll/ml, 0.125–0.5 lg/ml and0.125–05 ll/ml, respectively. The results showed thatdoses of MIC produced a greater anti-biofilm influencethan 0.5, 0.25 and 0.125 MIC. In the presence of essentialoil (MIC), the mean biofilm formation value was equal to67 ± 5.5 % for P. aeruginosa MU 188, and essential oil(MIC) inhibition exceeds 60 % for P. aeruginosa biofilms. The results also showed that carvacrol (MIC) was able toinduce an inhibition 72.9 ± 4.1 % for S.aureus (MU 40)biofilm. In addition, thymol (MIC) showed 68.6 ± 5.3 %reduction in biofilm formation of P. fluorescens MU 181. This study demonstrated the antimicrobial and antibiofilmactivity of T. sipyleus BOISS. subsp. sipyleus BOISS. var. davisianus RONNIGER essential oil and points out theexceptional efficiency of thymol and carvacrol, whichcould represent candidates in the treatment of Pseudomonasand Staphylococcus biofilms.

ON THE SEQUENCES RELATED TO FIBONACCI AND LUCAS NUMBERS

OZGUR NIHAL YILMAZ Korean Mathematical Society 2005 대한수학회지 Vol.42 No.1

In this paper, we obtain some properties of the sequences $U^{q}_n\;and\;V^{q}_n$ introduced in [6]. We find polynomial representations and formulas of them. For q = 5, $U^{5}_n$ is the Fibonacci sequence $F_n\;and\;V^{5}_n$ is the Lucas sequence $L_n$.

Harmony Search Algorithm for Continuous Network Design Problem with Link Capacity Expansions

Ozgur Baskan 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.1

The Continuous Network Design Problem (CNDP) deals with determining the set of link capacity expansions and the corresponding equilibrium link flows which minimizes the system performance index defined as the sum of total travel times and investment costs of link capacity expansions. In general, the CNDP is characterized by a bilevel programming model, in which the upper level problem is generally to minimize the total system cost under limited expenditure, while at the lower level problem, the User Equilibrium (UE)link flows are determined by Wardrop’s first principle. It is well known that bilevel model is nonconvex and algorithms for finding global or near global optimum solutions are preferable to be used in solving it. Furthermore, the computation time is tremendous for solving the CNDP because the algorithms implemented on real sized networks require solving traffic assignment model many times. Therefore, an efficient algorithm, which is capable of finding the global or near global optimum solution of the CNDP with less number of traffic assignments, is still needed. In this study, the Harmony Search (HS) algorithm is used to solve the upper level objective function and numerical calculations are performed on eighteen link and Sioux Falls networks. The lower level problem is formulated as user equilibrium traffic assignment model and Frank-Wolfe method is used to solve it. It has been observed that the HS algorithm is more effective than many other compared algorithms on both example networks to solve the CNDP in terms of the objective function value and UE traffic assignment number.

The Central Dislocation of Femoral Head in the Transverse and Both Column Acetabular Fractures: Is It Really Medialized?

( Ozgur Selek ),( Ahmet Y. Sarlak ) 대한고관절학회 2017 Hip and Pelvis Vol.29 No.3

Purpose: We hypothesized that the central dislocation of the femoral head does generally not occur in transverse acetabular fractures, although it does usually occur in both column fractures. Material and Methods: Fifty-two transverse and both column acetabular fracture cases were evaluated retrospectively. The distances between (a) the sciatic notch on the fracture side and the vertical axis of the pelvis (VA line) and (b) the contralateral intact sciatic notch and the VA line were measured. The a/b ratio corresponded to the superior iliac segment displacement or rotation. The ratio of the distance between the fracture side femoral head and the VA line (c) and the distance between the contralateral intact femoral head and the VA line (d) corresponded to the femoral head displacement. The width of ischium (e) on fractured side and (f) contralateral side were measured. The e/f ratio increment reflected ischiadic fragment mobility. Results: The median value of femoral head displacement (c/d) of the transverse fracture group (n=25) was 1.02 (1.000-1.07). Ischiadic fragment rotation (e/f ratio) of the transverse fracture group was 1.000. The median value of femoral head displacement (c/d) of the both column fractures (n=27) was 0.78 (0.64-0.85). Ischiadic fragment rotation (e/f ratio) of the both-column group was 1.15 (1.06-1.23). The differences between groups according to measurements were statistically significant. Conclusion: In contrary to Letournel description, our findings showed no medialization of femoral head in transverse acetabular fractures in general. This might be an illusion resulting from external rotation of the superior iliac segment.

Numerical Modeling of the Seismic Racking Behavior of Box Culverts in Dry Cohesionless Soils

Ozgur L. Ertugrul 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.5

In this study, dynamic behavior and lateral earth pressures on box shaped culverts buried in dry cohesionless soils were investigated through validated numerical analyses. Two dimensional plane strain finite difference models of 4m-high box culverts with different wall flexibilities were analyzed using FLAC-2D Finite Difference Code. The effect of relative flexibility on the dynamic racking displacements of the structure was investigated by modifying dynamic shear modulus of the cohesionless soil and structural attributes of the models. Shear strains, horizontal accelerations and wall deformations as well as lateral dynamic earth pressures at various points on the culvert were investigated through the numerical analyses. Results of the numerical analyses were validated with those of a previous centrifuge modeling study. Racking deformations of the numerical culvert models are found to be in agreement with the centrifuge test data. Dynamic lateral pressures acting on the side walls increase as the wall flexibility ratio decreases. Dynamic force on the sidewalls of the box culvert may reach up to 2.8 times the at-rest lateral earth load for the stiff prototype, whereas for the flexible prototype, this value is only 1.6 times the static earth load.

Employing variable impedance (stiffness/damping) hybrid actuators on lower limb exoskeleton robots for stable and safe walking trajectory tracking

Ozgur Baser,Hasbi Kizilhan,Ergin Kilic 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6

Compliant actuators are employed in exoskeleton robots instead of stiff actuators for safe human-robot interaction. In parallel with this idea, we previously constructed a biomimetic compliant exoskeleton robot (BioComEx). In this study, to provide more stable and safe trajectory tracking even under disturbances, magneto-rheological (MR) brakes were added to all joints of BioComEx as variable damping actuators and a PID+D controller was proposed. To evaluate the robot and controller, first, BioComEx was hung on a platform and the controller was applied without device user under external forces. This primary test results showed that the proposed design and controller can effectively minimize disturbance effects and consequently reduce trajectory tracking oscillations. In the rest of the study, the similar control experiments were repeated with a user who has unilateral lower limb movement disorders. In these experiments, the movements of the user's healthy leg were detected by force feedback impedance control algorithm and then were used as reference for the impaired leg with walking cycle delay in real time. The secondary test results showed that the variable impedance exoskeleton robot design with PID+D controller can ensure effective walking assistance for the impaired human legs.