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RISS 인기검색어
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- 저자 : Okan Karahan (검색결과 3 건)
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Effects of Milled Cut Steel Fibers on the Properties of Concrete
Okan Karahan,Erdogan Ozbay,Cengiz D. Atis,Mohamed Lachemi,Khandaker M. A. Hossain 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.7
This study presents the mechanical and transport properties of milled cut steel fiber reinforced concretes (MCSFRC). Properties studied include unit weight, workability, compressive strength, flexural strength, splitting tensile strength, bond strength, water absorption, water porosity, water sorptivity, rapid chloride ion permeability and drying shrinkage of concrete. Mixtures with a waterbinder ratio of 0.40, total binder content of 500 kg/m3 and milled cut steel fiber content of 0, 0.25, 0.50 and 1.00% by concrete volume were produced and tested. The laboratory results showed a slight reduction in compressive strength with the use of milled cut steel fiber. On the other hand milled cut steel fibers significantly improved the tensile strength and decreased the drying shrinkage. Although no significant increase was observed in the absorption, porosity and sorptivity, chloride ion permeability increased drastically with the increase of milled cut steel fiber content.
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Cahit Bilim,Okan Karahan,Duran Ati,Serhan lkentapar 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.3
This paper reports the results of an investigation on the influences of admixtures and curing conditions on some properties ofAlkali-Activated Slag (AAS) mixtures with no cement. In the study, Shrinkage-Reducing (SRA) and superplasticizing and setretarding(WRRe) admixtures were used. For the slag activation, sodium metasilicate was used at two sodium concentrations, 4%and 6% by mass of slag. Setting time, flow loss of fresh mixtures, and shrinkage strain, carbonation, flexural and compressivestrength of hardened mixtures were measured. The test results showed that the admixtures generally had no impact on the settingtimes of AAS pastes. WRRe increased the flow rate of AAS mortars while SRA partially affected the flow values of AAS mortars. This paper reports the results of an investigation on the influences of admixtures and curing conditions on some properties ofAlkali-Activated Slag (AAS) mixtures with no cement. In the study, Shrinkage-Reducing (SRA) and superplasticizing and setretarding(WRRe) admixtures were used. For the slag activation, sodium metasilicate was used at two sodium concentrations, 4%and 6% by mass of slag. Setting time, flow loss of fresh mixtures, and shrinkage strain, carbonation, flexural and compressivestrength of hardened mixtures were measured. The test results showed that the admixtures generally had no impact on the settingtimes of AAS pastes. WRRe increased the flow rate of AAS mortars while SRA partially affected the flow values of AAS mortars. WRRe and SRA did not produce an important difference on the carbonation depths of AAS mortars. However, WRRe and especiallySRA admixtures decreased the shrinkage values of AAS mortars. Additionally, curing conditions had a significant effect on themechanical behavior in the hardened state of AAS mortars compared to Normal Portland Cement (NPC) mortars, and the strengthdevelopment of AAS mortars at early ages was very fast in comparison with NPC mortars when subjected to elevated temperature.
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Long-term results of radiofrequency and microwave ablation of colorectal cancer liver metastasis
Ahmet Gürkan Erdemir,Sevilay Karahan,Emre Ünal,Türkmen Turan Çiftçi,Devrim Akıncı,Şuayib Yalçın,Okan Akhan 소화기인터벤션의학회 2023 International journal of gastrointestinal interven Vol.12 No.3
Background: Radiofrequency ablation (RFA) or microwave ablation (MWA) is effective for colorectal cancer liver metastases. We aimed to investigate the impact of different variables on survival. Methods: Sixty-four patients (142 lesions) who underwent thermoablation between January 2007 and January 2019 were retrospectively analyzed. The overall survival (OS) and liver progression-free survival (Li-PFS) were compared using Kaplan-Meier analysis. Univariable and multivariable Cox-regression were done to identify prognostic factors. Results: No significant difference was found between median OS (59.39 months) and Li-PFS (41.22 months) of patients who received MWA (n = 33); and median OS (61.00 months) and Li-PFS (53.43 months) of patients who received RFA (n = 31) (OS: P = 0.697; Li-PFS: P = 0.122). The median OS and Li-PFS were significantly decreased with lung metastases and K-ras mutations (P < 0.001). There was no correlation between prior systemic chemotherapy (n = 25) and both outcome parameters (OS: P = 0.613; Li-PFS: P = 0.665). No significant difference was observed in patients with lesions less than 30 mm diameter (n = 44) whether they received prior systemic chemotherapy (n = 17) or not (n = 27) (OS: P = 0.27; Li-PFS: P = 0.42). Similarly, in patients with a lesion of 3–5 cm diameter (n = 20; eight of them had prior chemotherapy), there was no correlation for both outcomes (OS: P = 0.069; Li-PFS: P = 0.71). The most important prognostic factor was concomitant lung metastases (hazard ratio = 3.689, P = 0.002). Conclusion: Concomitant lung metastasis and mutant K-ras were associated with shorter survival. Survival did not differ significantly regarding thermoablation technique or prior systemic chemotherapy. However, in the patient group with lung metastases, curative treatments had better survival than patients who received chemotherapy only. Additional therapeutic options should be considered in patients with concomitant lung metastasis.
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