15 Park Row New York City - 120 Years Later, Still Relevant in Contextualism and Sustainability

Karahan, Beyhan Council on Tall Building and Urban Habitat Korea 2020 International journal of high-rise buildings Vol.9 No.1

After the 1884 Home Insurance building in Chicago and 1889 Tower building in New York, 15 Park Row became the tallest building in the USA in 1899 and it held this record for nine years. Completed just before the arrival of the 20^th century, this building deserves to be recognized for the sophistication of its architecture with respect to contextual understanding of the 19^th century historic texture in Lower Manhattan, its uniquely economical floor plans, and its use of natural ventilation and daylight. The compositional techniques using the proportional analysis of its context reflect the highest level of architectural education of its time by its architect Robert H. Robinson. In addition, it also offers a unique glimpse to the state-of-the-art technology of its time regarding its structure, its use of movement systems that was capable of serving 4000 users.

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.

Determining Rainfall-Intensity-Duration-Frequency Relationship Using Particle Swarm Optimization

Halil Karahan 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.4

This study proposes a Particle Swarm Optimization (PSO) algorithm to model the Rainfall-Intensity-Duration-Frequency (RIDF)relationship. The study is carried out under two scenarios. In scenario I, a data set with a length of 50 years is used. In Scenario II, the data set is extended to 68 years by adding the values of the recent 18 years. Scenario I is used for testing the robustness of the proposed PSO-RIDF model. The PSO-RIDF algorithm gives the same objective function value for different runs and this shows that the proposed algorithm is robust. Scenario II is used to investigate the influence of data length on model performance. It has been observed that the proposed PSO-RIDF model gives the same performance results as that of the Genetic Algorithm (GA) according to various error evaluation criteria. The PSO-RIDF model shows better performance than GA formulas when the number of parameters increases. It has also been observed that the length of the data set and the chosen formulation are influential on model performance. The weighting parameters of the RIDF model may be determined with PSO algorithm in one-stage instead of any statistical computations and/or trial-error procedure.

An iterative method for common solution to various problems

IBRAHIM KARAHAN,SAFEER HUSAIN KHAN 장전수학회 2019 Advanced Studies in Contemporary Mathematics Vol.29 No.3

In this paper, we introduce a new iterative method to …nd a common solution of a generalized mixed equilibrium problem, a vari- ational inequality problem and a hierarchical …xed point problem for demicontinuous nearly nonexpansive mappings. We prove that our method converges strongly to a common solution of all above problems. It is worth noting that Main Theorem is proved without usual demiclosed- ness condition. As our iterative method generalizes several methods, the results here improve and extend many recent results.

Vibration analysis of a beam on a nonlinear elastic foundation

M.M. Fatih Karahan,Mehmet Pakdemirli 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.2

Nonlinear vibrations of an Euler-Bernoulli beam resting on a nonlinear elastic foundation are discussed. In search of approximate analytical solutions, the classical multiple scales (MS) and the multiple scales Lindstedt Poincare (MSLP) methods are used. The case of primary resonance is investigated. Amplitude and phase modulation equations are obtained. Steady state solutions are considered. Frequency response curves obtained by both methods are contrasted with each other with respect to the effect of various physical parameters. For weakly nonlinear systems, MS and MSLP solutions are in good agreement. For strong hardening nonlinearities, MSLP solutions exhibit the usual jump phenomena whereas MS solutions are not reliable producing backward curves which are unphysical.

Evaluating Focal 18F-FDG Uptake in Thyroid Gland with Radiomics

Aksu Ayşegül,Karahan Şen Nazlı Pınar,Acar Emine,Çapa Kaya Gamze 대한핵의학회 2020 핵의학 분자영상 Vol.54 No.5

Purpose The aim of this study was to evaluate the ability of 18F-FDG PET/CT texture analysis to predict the exact pathological outcome of thyroid incidentalomas. Methods 18F-FDG PET/CT images between March 2010 and September 2018 were retrospectively reviewed in patients with focal 18F-FDG uptake in the thyroid gland and who underwent fine needle aspiration biopsy from this area. The focal uptake in the thyroid gland was drawn in 3D with 40% SUVmax threshold. Features were extracted from volume of interest (VOI) using the LIFEx package. The features obtained were compared in benign and malignant groups, and statistically significant variables were evaluated by receiver operating curve (ROC) analysis. The correlation between the variables with area under curve (AUC) value over 0.7 was examined; variables with correlation coefficient less than 0.6 were evaluated with machine learning algorithms. Results Sixty patients (70% train set, 30% test set) were included in the study. In univariate analysis, a statistically significant difference was observed in 6 conventional parameters, 5 first-, and 16 second-order features between benign and malignant groups in train set (p < 0.05). The feature with the highest benign-malignant discriminating power was GLRLMRLNU (AUC:0.827). AUC value of SUVmax was calculated as 0.758. GLRLMRLNU and SUVmax were evaluated to build a model to predict the exact pathology outcome. Random forest algorithm showed the best accuracy and AUC (78.6% and 0.849, respectively). Conclusion In the differentiation of benign-malignant thyroid incidentalomas, GLRLMRLNU and SUVmax combination may be more useful than SUVmax to predict the outcome.

Effectiveness of Intravitreal Ranibizumab for Diabetic Macular Edema with Serous Retinal Detachment

Mahmut Kaya,Eyyup Karahan,Taylan Ozturk,Nilufer Kocak,Suleyman Kaynak 대한안과학회 2018 Korean Journal of Ophthalmology Vol.32 No.4

Purpose: To evaluate the effectiveness of intravitreal injection of ranibizumab (IVR) in treating diabetic macular edema (DME) with serous retinal detachment (SRD) based on spectral domain optical coherence tomography (SD-OCT) patterns. Methods: One hundred thirty-four eyes of 134 patients with DME who underwent SD-OCT evaluation were included in this study. We retrospectively analyzed the medical records of patients who received IVR for the treatment of DME. Their eyes were classified into three groups according to the following SD-OCT features: SRD, diffuse retinal thickness and cystoid macular edema. The three groups were compared regarding changes in best-corrected visual acuity and central foveal thickness (CFT) after IVR. Results: The mean age was 61.4 ± 9.2 years (range, 44 to 81 years). The average length of the follow-up period was 9.4 ± 3.4 months (range, 6 to 24 months). The mean CFT value was significantly reduced in all groups (p < 0.001) after treatment. Increases in best-corrected visual acuity were statistically significant for the diffuse retinal thickness and cystoid macular edema groups (p < 0.001 and p < 0.001, respectively). However, there was no significant improvement after IVR injection in the SRD group (p = 0.252). In the SRD group, patients with ellipsoid zone disruption and external limiting membrane disruption demonstrated poorer visual gains at the last follow-up visit (p < 0.005 and p = 0.002, respectively). Conclusions: A significant reduction in CFT with required IVR injections in DME with SRD was achieved but was accompanied by a worse functional outcome in the SRD group. The presence of subretinal fluid on SD-OCT in study eyes may be a poor prognostic factor for visual acuity.

[신진연구자] 수처리와 가스 분리를 위한 대면적 산화그래핀 막의 제조

양은태,H. Enis Karahan,Kunli Goh,Chong Yang Chuah,Rong Wang,배태현 대한환경공학회 2019 대한환경공학회 학술발표논문집 Vol.2019 No.12

The effect of repeated porcelain firings on corrosion resistance of different dental alloys

Ali Riza Tuncdemir,Ismail Karahan,Serdar Polat,Meral Arslan Malkoc,Mehmet Dalkiz 대한치과보철학회 2013 The Journal of Advanced Prosthodontics Vol.5 No.1

PURPOSE. The aim of this study was to evaluate the effects of repeated porcelain firing process on the corrosion rates of the dental alloys. MATERIALS AND METHODS. Cr-Co, Cr-Ni and Pd-Ag alloys were used for this study. Each metal supported porcelain consisted of 30 specimens of 10 for 7, 9 and 11 firing each. Disc-shaped specimens 10 mm diameter and 3 mm thickness were formed by melting alloys with a propane-oxygen flame and casted with a centrifuge casting machine and then with the porcelain veneer fired onto the metal alloys. Corrosion tests were performed in quintuplicate for each alloy (after repeated porcelain firing) in Fusayama artificial saliva solution (pH = 5) in a low thermal-expansion borosilicate glass cell. Tamhane and Sheffe test was used to compare corrosion differences in the results after repeated firings and among 7, 9 and 11 firing for each alloy. The probability level for statistical significance was set at α=0.05. RESULTS. The corrosion resistance was higher (30 mV), in case of 7 times firing (Commercial). On the other hand, it was lower in case of 11 times firing (5 mV) (P<.05). Conclusion. Repeated firings decreased corrosion resistance of Pd-Ag, Cr-Co and Cr-Ni alloys. The Pd-Ag alloy exhibited little corrosion in in vitro tests. The Cr-Ni alloy exhibited higher corrosion resistance than Cr-Co alloys in in vitro tests.

Effects of Chemical Admixtures and Curing Conditions on some Properties of Alkali-Activated Cementless Slag Mixtures

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.