Raw and pyrolyzed (with and without melamine) graphene nanoplatelets with different surface areas as PEM fuel cell catalyst supports

Öztürk Ayşenur,Bayrakçeken Yurtcan Ayşe 한국탄소학회 2021 Carbon Letters Vol.31 No.6

Platinum (Pt) catalysts dispersed on carbon-based support materials are generally used in the polymer electrolyte membrane (PEM) fuel cells. In this study, commercial graphene nanoplatelets (GNPs), with diferent surface areas (320, 530, 800 m2 g−1), were used as catalyst supports in PEM fuel cells. These GNPs were also pyrolyzed under the inert atmosphere, with and without melamine, as the nitrogen (N) source. Various characterizations (Elemental analysis, FTIR, Raman spectroscopy, BET, TEM, HRTEM, SAED, XRD, TGA, ICP-MS, contact angle measurement, CV, ORR, chronoamperometry, EIS, PEM fuel cell performance test) were performed for the detailed analysis of Pt/GNPs. Based on the three-electrode cell system, the lowest electrochemical surface area (ECSA) loss (29.9%), Pt mass activity loss (20.3%) and overall (charge and mass) resistance (42.2 Ω) were obtained with the Pt/M-530 catalyst. According to the in-situ PEM fuel cell performance results, the specifc peak power density was recorded as (450 mW mg Pt−1) for the Pt/R-530 catalyst, which has also the second most hydrophobic catalyst layer surface with the 146.5°±1.28° contact angle value. On the heels of Pt/R-530, the two best performances also belong to the Pt/M-530 (391 mW mg Pt−1) and Pt/P-530 (378 mW mg Pt−1) catalysts of the same group.

Effect of solvent exchange on the properties of carbon xerogel and carbon xerogel/polypyrrole composites for supercapacitors

Samancı Meryem,Daş Elif,Yurtcan Ayşe Bayrakçeken 한국탄소학회 2021 Carbon Letters Vol.31 No.6

Carbon xerogels (CXs) with three-dimensional (3D) structure, unusual surface, physical, electrical and mechanical properties and their electrically conductive polymer polypyrrole (PPy) composites were synthesized as electrode materials for supercapacitors. The efect of diferent resorcinol/formaldehyde (R/C) ratios, whether solvent exchange with or without acetone and polypyrrole addition on the physicochemical (FTIR, XRD, BET, SEM and TGA) and electrochemical properties (CV, 1000 cycles) of the synthesized materials were investigated. It was observed that the R/C ratio and the solvent exchange process prior to drying afect the specifc surface areas and the pore size distributions, thereby positively afecting the specifc capacitance. PPy flm thickness was observed to be efective in the specifc capacitance of the electrode in PPy composite synthesis. Among the synthesized materials, the highest specifc capacitance values belong to polypyrrole/carbon xerogel composites. As a result of the analysis and calculations, it was found that the highest specifc capacitance belongs to CX2/PPy composite with 599 Fg−1 at 5 mVs−1. CX2/PPy composite has been found to have a capacitance retention rate of 80.30% at the end of 1000 cycles.

The Economics of Cloud Computing

( Ergin Bayrak ),( John P. Conley ),( Simon Wilkie ) 한국경제학회 2011 The Korean Economic Review Vol.27 No.2

Cloud computing brings together several existing technologies including service oriented architecture, distributed grid computing, virtualization, and broadband networking to provide software, infrastructure, and platforms as services. Under the old IT model, companies built their own server farms designed to meet peak demand using bundled hardware and software solutions. This was time consuming, capital intensive and relatively inflexible. Under the cloud computing model, firms can rent as many virtual machines as they need at any given time, and then either design or use off-the-shelf solutions to integrate company-wide data in order to easily distribute access to users both within and outside of the company firewall. This converts fixed capital costs into variable costs, prevents under and over provisioning, and allows minute by minute flexibly. Consumers are also increasingly turning to the cloud for computing service through such applications as Gmail, Pandora, and Facebook. The purpose of this paper is to discuss this new and transformative technology, survey the existing economics literature on the subject, and suggest potential directions for new research.

Analysis of Changes in the Glomerular Filtration Rate as Measured by the Cockroft-Gault Formula in the Early Period after Percutaneous Nephrolithotomy

Omer Bayrak,Ilker Seckiner,Sakip M. Erturhan,Sedat Mizrak,Ahmet Erbagci 대한비뇨의학회 2012 Investigative and Clinical Urology Vol.53 No.8

Purpose: We aimed to analyze the changes in kidney function during the postoperative early period caused by the application of percutaneous nephrolithotomy (PNL), which is commonly used in kidney stone surgery. Materials and Methods: PNL was performed in 80 patients (48 men, 32 women) with kidney stones. The mean age of the patients was 43.71 years (range, 18 to 71 years). Preoperative and postoperative values for stone size, glomerular filtration rate (GFR), serum creatinine, urea, electrolytes (Na, K, Cl), and Hb were compared in 80 patients in whom PNL surgery was performed. The formula of Cockroft-Gault was used to calculate the GFR during the early postoperative period (72 to 96 hours). Results: Statistically significant decreases after PNL were observed in average stone size (preoperative, 627.75±375.10 mm2; postoperative, 81.70±16.15 mm2), serum urea (preoperative, 38.40±17.26 mg/dl; postoperative, 33.28±16.98 mg/dl), and creatinine (preoperative, 1.03±0.53 mg/dl; postoperative, 0.97±0.55 mg/dl) and an increase was observed in GFR (preoperative, 104.30±37.30 ml/min; postoperative, 112.38±40.1 ml/min). No changes were detected in the serum electrolyte values (Na, K, Cl). Multiple access, operation time, and type of lithotripter did not have any significant effects on the change in the GFR. Conclusions: In light of our results, PNL for kidney stone operations appears to be a reliable and efficient method that provides recovery of kidney functions in the early post-operative period by increasing the GFR and with high stone-free rates. Purpose: We aimed to analyze the changes in kidney function during the postoperative early period caused by the application of percutaneous nephrolithotomy (PNL), which is commonly used in kidney stone surgery. Materials and Methods: PNL was performed in 80 patients (48 men, 32 women) with kidney stones. The mean age of the patients was 43.71 years (range, 18 to 71 years). Preoperative and postoperative values for stone size, glomerular filtration rate (GFR), serum creatinine, urea, electrolytes (Na, K, Cl), and Hb were compared in 80 patients in whom PNL surgery was performed. The formula of Cockroft-Gault was used to calculate the GFR during the early postoperative period (72 to 96 hours). Results: Statistically significant decreases after PNL were observed in average stone size (preoperative, 627.75±375.10 mm2; postoperative, 81.70±16.15 mm2), serum urea (preoperative, 38.40±17.26 mg/dl; postoperative, 33.28±16.98 mg/dl), and creatinine (preoperative, 1.03±0.53 mg/dl; postoperative, 0.97±0.55 mg/dl) and an increase was observed in GFR (preoperative, 104.30±37.30 ml/min; postoperative, 112.38±40.1 ml/min). No changes were detected in the serum electrolyte values (Na, K, Cl). Multiple access, operation time, and type of lithotripter did not have any significant effects on the change in the GFR. Conclusions: In light of our results, PNL for kidney stone operations appears to be a reliable and efficient method that provides recovery of kidney functions in the early post-operative period by increasing the GFR and with high stone-free rates.

A case report overlapped vaccine and COVID-19 in disseminated atherosclerosis

Vecihe Bayrak 대한백신학회 2023 Clinical and Experimental Vaccine Research Vol.12 No.2

Coronavirus disease 2019 (COVID-19) has become a part of our lives now and we have no more effective way of coping than a vaccine. COVID-19 is a disease that causes severe thrombosis outside the respiratory tract. Vaccines also protect us in this respect, but in some rare cases, thrombosis has been found to develop after vaccination (much less frequently than COVID-19). What was interesting in our case was that it showed how a disaster could happen under three factors that predispose to thrombosis. A 65-year-old female patient with disseminated atherosclerosis was admitted to the intensive care unit with complaints of dyspnea and dysphasia. In the evening of the day, the patient had the vaccination 2 weeks ago, she had active COVID-19. On examination, lower extremity pulses could not be detected. The patient’s imaging and blood tests were performed. Multiple complications such as embolic stroke, venous and arterial thrombosis, pulmonary embolism, and pericarditis were observed in the patient. This case may give consideration to anticoagulant therapy studies. We give effective anticoagulant therapy in the presence of COVID-19 in patients at risk of thrombosis. Can anticoagulant therapy be considered after vaccination in patients at risk of thrombosis such as disseminated atherosclerosis?

Kinetic study on the leaching of calcined magnesite in gluconic acid solutions

Bahar Bayrak,Hanifi Sarac,Oral Lac¸in 한국공업화학회 2010 Journal of Industrial and Engineering Chemistry Vol.16 No.3

A kinetic study on the leaching of calcinedmagnesite in aqueous gluconic acid solutionswas investigated in batch reactor employing the parameters of particle size, temperature, stirring speed, solid–liquid ratio and acid concentration. A mathematical model was evaluated for the rate increased with decreasing particle size and increasing temperature and initially, the leaching in terms of acid concentration and then fell with increasing concentration. It was found in the study that stirring speed was not effective on leaching rate. The leaching rate decreases as solid–liquid ratio increases. It was shown that the mathematical model for calcined magnesite particle was:1:9041 lnðð1 XBÞ1=3 þ 1:157Þ þ 0:952 lnðð1 XBÞ2=3 1:156ð1 XBÞ1=3 þ 1:338Þ3:298 arctanð0:577ð1:73ð1 XBÞ1=3 1ÞÞ ¼3bkSCA0rBR tDissolution curves were evaluated in order to test shrinking core models for fluid–solid systems. Consequently, it was determined that the leaching rate is controlled by surface chemical reaction. In addition, the fact that dissolution was controlled by the surface chemical reaction was also supported with the relationship between the rate constant and the particle radius. The activation energy of the process was determined to be 32.88 kJ mol1. 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Reliability of Percutaneous Nephrolithotomy in Pediatric Patients: Comparison of Complications With Those in Adults

Omer Bayrak,Sakip Erturhan,Ilker Seckiner,Muharrem Baturu,Ismail Basmaci,Ahmet Erbagci 대한비뇨의학회 2013 Investigative and Clinical Urology Vol.54 No.6

Purpose: To assess the reliability of percutaneous nephrolithotomy (PNL) in pediatric patients by comparing complications between pediatric patients and adults by use of the modified Clavien grading system. Materials and Methods: The data of 74 pediatric (0 to 16 years) and 535 adult (17 years and older) patients who underwent PNL owing to kidney stone disease between January 2005 and December 2011 were analyzed retrospectively. The complications in the pediatric and adult patients were classified in five grades according to the modified Clavien system. Results: The most frequent cause of grade I complications was fever requiring antipyretics,which was seen in 4 pediatric patients (5.4%) and 30 adult patients (5.6%). Grade II complications (blood transfusions, <12 hours urinary leakage) were observed in 11 pediatric patients (14.8%) and 80 adult patients (14.9%). Grade III complications were also seen in 6 pediatric patients (8.1%) (grade IIIb; D-J catheter implantation under general anesthesia) and 78 adult patients (14.5%) (grade IIIa; D-J catheter implantation and angio-embolization under local anesthesia). There was no statistically significant difference between the two groups in terms of grade I, II, or III complications (p>0.05). Colonic injury occured in one patient (1.3%) in the pediatric group (grade IVa). In the adult group, one patient (0.2%) died as the result of myocardial infarction (grade V). Conclusions: Thanks to technological developments and minimalization of the equipment used, when indicated, pediatric patients can be safely treated with PNL with low complication rates similar to those in adult patients.

Acute Lymphoblastic Leukemia Presented as Multiple Breast Masses

Ilkay Koray Bayrak,Turkay Yalin,Zafer Ozmen,Tolga Aksoz,Roula Doughanji 대한영상의학회 2009 Korean Journal of Radiology Vol.10 No.5

Breast metastases in cases leukemia are very rare and occur primarily in patients with acute myeloid leukemia. We report the involvement of breast metastases in a 30-year-old woman with acute T cell lymphoblastic leukemia. The patient’s mammograms revealed an extremely dense pattern with ill-defined, denser mass-like lesions in both breasts. A bilateral breast ultrasonographic evaluation revealed lobular-shaped and partly ill-defined hypoechoic masses with a multi-septated nodular (mottled) appearance.

The Effect of Insulin Like Growth Factor-1 on Recovery of Facial Nerve Crush Injury

Asuman Feda Bayrak,Yuksel Olgun,Ayla Ozbakan,Safiye Aktas,Can Ahmet Kulan,Gonca Kamaci,Emine Demir,Osman Yilmaz,Levent Olgun 대한이비인후과학회 2017 Clinical and Experimental Otorhinolaryngology Vol.10 No.4

Objectives. The aim of this study is to investigate the efficacy of locally applied insulin-like growth factor 1 (IGF-1) on the recovery of facial nerve functions after crush injury in a rabbit model. Methods. The rabbits were randomly assigned into three groups. Group 1 consisted of the rabbits with crush injury alone; group 2, the animals applied saline solution onto the crushed facial nerve and group 3, IGF-1 implemented to the nerve in the same manner. Facial nerve injury was first electrophysiologically studied on 10th and 42nd days of the procedure. The damage to the facial nerves was then investigated histopathologically, after sacrification of the animals. Results. In the electrophysiological study, compound muscle action potential amplitudes of the crushed nerves in the second group were decreased. In pathological specimens of the first and second groups, the orders of axons were distorted; demyelination and proliferation of Schwann cells were observed. However, in IGF-1 treated group axonal order and myelin were preserved, and Schwann cell proliferation was close to normal (P<0.05). Conclusion. Local application of IGF-1 in a slow releasing gel was found efficacious in the recovery of the facial nerve crush injury in rabbits. IGF-1 was considered worthy of being tried in clinical studies in facial nerve injury cases.

A Comparison of Low-Dose and Normal-Dose Gadobutrol in MR Renography and Renal Angiography

Ilkay Koray Bayrak,Zafer Ozmen,Mehmet Selim Nural,Murat Danaci,Baris Diren 대한영상의학회 2008 Korean Journal of Radiology Vol.9 No.3

Objective: It has been advocated that a reduced injection volume with highly concentrated (1 M) contrast material can produce a sharper bolus peak and an increased intravascular first-pass gadolinium concentration when compared with the use of a lower concentration (0.5 M). A higher concentration would also cause a reduction in dose. The purpose of our study was to test the use of a low dose (0.05 mmol/kg) of gadobutrol in magnetic resonance renography and angiography and compare the findings with a dose of 0.1 mmol/kg. Materials and Methods: One-hundred-thirty-four patients referred for magnetic resonance angiography for suspected renovascular disease participated in the study. Contrast enhanced MR renography and angiography were performed after administration of a bolus of 0.1 mmol/kg or 0.05 mmol/kg gadobutrol in randomized patients. The relative signal intensity-time curves of the aorta, peripheral cortex and parenchyma, were obtained. Two radiologists evaluated the angiographic images and evaluated the quality of angiography. Results: The signal intensity with a low dose of gadobutrol was significantly lower in early phases, in the peripheral cortex (for 36, 54, 72 and 90 seconds), the parenchyma (for 36, 54, 72 seconds) and the aorta (for 18, 36, 54, 72 seconds). The decreases in the early phase obtained with a low dose of gadobutrol caused blunter time intensity curves. The difference in the quality scores of the readers for the angiographic images for the use of the two different doses was not statistically significant (p > 0.05). Conclusion: A lower dose of gadobutrol can be used for MR renal angiography, but for MR renography the normal dose should be used. Objective: It has been advocated that a reduced injection volume with highly concentrated (1 M) contrast material can produce a sharper bolus peak and an increased intravascular first-pass gadolinium concentration when compared with the use of a lower concentration (0.5 M). A higher concentration would also cause a reduction in dose. The purpose of our study was to test the use of a low dose (0.05 mmol/kg) of gadobutrol in magnetic resonance renography and angiography and compare the findings with a dose of 0.1 mmol/kg. Materials and Methods: One-hundred-thirty-four patients referred for magnetic resonance angiography for suspected renovascular disease participated in the study. Contrast enhanced MR renography and angiography were performed after administration of a bolus of 0.1 mmol/kg or 0.05 mmol/kg gadobutrol in randomized patients. The relative signal intensity-time curves of the aorta, peripheral cortex and parenchyma, were obtained. Two radiologists evaluated the angiographic images and evaluated the quality of angiography. Results: The signal intensity with a low dose of gadobutrol was significantly lower in early phases, in the peripheral cortex (for 36, 54, 72 and 90 seconds), the parenchyma (for 36, 54, 72 seconds) and the aorta (for 18, 36, 54, 72 seconds). The decreases in the early phase obtained with a low dose of gadobutrol caused blunter time intensity curves. The difference in the quality scores of the readers for the angiographic images for the use of the two different doses was not statistically significant (p > 0.05). Conclusion: A lower dose of gadobutrol can be used for MR renal angiography, but for MR renography the normal dose should be used.