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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Conditional law and occupation times of two-sided sticky Brownian motion(Elsevier, 2020) Department of Mathematics; Çağlar, Mine; Can, Buğra; Faculty Member; Department of Mathematics; College of Sciences; 105131; N/ASticky Brownian motion on the real line can be obtained as a weak solution of a system of stochastic differential equations. We find the conditional distribution of the process given the driving Brownian motion, both at an independent exponential time and at a fixed time t>0. As a classical problem, we find the distribution of the occupation times of a half-line, and at 0, which is the sticky point for the process.Publication Open Access Effectiveness of posterior structures in the development of proximal junctional kyphosis following posterior instrumentation: a biomechanical study in a sheep spine model(Elsevier, 2019) Akgül, Turgut; Sarıyılmaz, Kerim; Özkunt, Okan; Dikici, Fatih; Yazıcıoğlu, Önder; N/A; Korkmaz, Murat; Doctor; School of MedicineIntroduction: proximal junctional kyphosis – PJK has been defined by a 10 or greater increase in kyphosis at the proximal junction as measured by the Cobb angle from the caudal endplate of the uppermost instrumented vertebrae (UIV) to the cephalad endplate of the vertebrae 1 segments cranial to the UIV. In this biomechanical study, it is aimed to evaluate effects of interspinosus ligament complex distruption and facet joint degeneration on PJK development. Materials and methods: posterior instrumentation applied between T2 – T7 vertebrae using pedicle screws to randomly selected 21 sheeps, divided into 3 groups. First group selected as control group (CG), of which posterior soft tissue and facet joints are protected. In second group (spinosus group, SG) interspinosus ligament complex which 1 segment cranial to UIV has been transected, and third group (faset group-FG) was applied facet joint excision. 25 N, 50 N, 100 N, 150 N and 200 N forces applied at frequency of 5 Hertz as 100 cycles axial to the samples. Then, 250 N, 275 N and 300 N forces applied static axially. Interspinosus distance, kyphosis angle and discus heights was measured in radiological evaluation. Abnormal PJK was defined by a proximal junctional angle greater than 100 and at least 100 greater than the corresponding preoperative measurement. Results: in CG group, average interspinosus distance was 6,6 ± 1.54 mm and kyphosis angle was 2,2 ± 0.46° before biomechanical testing, and they were measured as 9,4 ± 1.21 mm and 3,3 ±0.44° respectively after forces applied to samples. In SG group, average interspinosus distance was 6,2 ± 1.72 mm and kyphosis angle was 2,7 ± 1.01° before experiment, and they were measured as 20,8 ± 5.66 mm and 15,1 ± 2.34° respectively after forces applied to samples. In FG group, average interspinosus distance was 4,8 ± 1.15 mm and kyphosis angle was −1 ± 4.14° before experiment, and they were measured as 11,1 ±1.96mm and 11 ± 2.87° respectively after forces applied to samples. In comparison to group CG, statistically significant junctional kyphosis was seen on both FG and SG group after statistical analysis. (p < 0.05). PJK was seen statistically significant more on SG group than FG group. (p < 0.05). Not any statistically significant difference was seen on measurement of disk distances among three groups. (p > 0.05) Conclusions: protecting interspinosus ligament complex and facet joint unity during posterior surgical treatment for spine deformation is vital to prevent PJK development. Based on our literature review, this is the first biomechanical study that reveals interspinosus ligament complex are more effective on preventing PJK development than facet joints.Publication Open Access Random assignment under weak preferences(Elsevier, 2009) Department of Economics; Yılmaz, Özgür; Faculty Member; Department of Economics; College of Administrative Sciences and Economics; 108638The natural preference domain for many practical settings of the assignment problems is the one in which agents are allowed to be indifferent between objects, the weak preference domain. Most of the existing work on assignment problems assumes strict preferences. There are important exceptions. but they provide solutions only to the assignment problems with a social endowment, where agents own objects collectively and there are no private endowments. We consider the general class of assignment problems with private endowments and a social endowment. Our main contribution is a recursive solution for the weak preference domain. Our solution satisfies individual rationality, ordinal efficiency and a recently introduced fairness axiom, no justified-envy.Publication Open Access Multi-level anterior cervical decompression in multi-level cervical spondylotic myelopathy without extending the corpus resection: a cadaveric study of a novel surgical technique(Turkish Neurosurgical Society, 2021) Saygı, Tahsin; Özdemir, Ömer; Evran, Şevket; Kayhan, Ahmet; Özbek, Muhammet Arif; Erkan, Buruç; Demirel, Nail; Özdoğan, Selçuk; Baran, Oğuz; Faculty Member; Koç University HospitalAim: to perform three-level decompression with a single-level corpectomy by modifying the fusion with anterior cervical corpectomy (ACC-F) method on a cadaver. Material and methods: the anterior cervical region of four whole-head cadavers was dissected. The corpectomy was performed under a surgical microscope with a MT4-20+ ultrasonic bone dissector (UBD) tip. Superior and inferior decompression were conducted and viewed with a 70 degrees neuroendoscope using two types (vertically and horizontally oriented) of specially designed 23 mm-long, 90 degrees-angled UBD tips. Results: after neck dissection and the removal of the thyroid and cricoid cartilages, C5 corpectomy and adjacent-level discectomies were performed. Following discectomy and corpectomy, superior and inferior decompression were conducted with specially designed UBD tips and viewed with a 70 degrees neuroendoscope. A three-level anterior cervical decompression was provided with a single-level corpectomy. Conclusion: this study demonstrated that two more level decompression is possible with a single-level corpectomy in the cervical region using the new technique.Publication Open Access The epidemiological and molecular characterization of vancomycin-resistant enterococci Isolated from rectal swab samples of hospitalized patients in Turkey(Clinical Laboratory, 2014) Çakırlar, Fatma Köksal; Karakullukçu, Asiye; Sirekbasan, Serhat; Bağdatlı, Yaşar; Department of Chemical and Biological Engineering; Barış, İbrahim; Kavaklı, İbrahim Halil; Teaching Faculty; Department of Chemical and Biological Engineering; College of Engineering; 111629; 40319Background: Vancomycin-resistant enterococci (VRE) are a serious problem all over the world. The present study was conducted to investigate antimicrobial resistance patterns, genotypes, clonal relationship, and virulence factors of VRE species isolated from rectal swab samples of hospitalized patients, patient's relatives, and medical staff at Istanbul University Cerrahpasa Medical School hospital. Methods: The VRE isolates were typed with an automated VITEK system and their antibiotic sensibilities were analysed by disc diffusion and Etest (R) method. The molecular characterization and clonal relationships were performed using a PCR method and virulence genes by sequence typing. Results: A total of 100 (10.3%) of the 971 patients were colonized with VRE. None of the investigated 25 patient's relatives and 45 medical staff carried VRE. All VRE strains were identified as E. faecium. They were vanA geno-type and originated from a single clone. VRE strains exhibited multi-drug resistance. High-level gentamicin-resistance was 93%. However, lower resistance rates were found for linezolid (40%) and quinopristin-dalfopristin (11%). The enterococcal surface protein gene esp was found positive in 87 of 100 isolates, and four strains were positive for the cylB (cytolysin) gene. Conclusions: The identification of VRE strains to the species level and detection of virulence genes will assist in infection control practices.Publication Open Access Rosiglitazone-induced changes in the oxidative stress metabolism and fatty acid composition in relation with trace element status in the primary adipocytes(Sciendo, 2019) N/A; Aydemir, Duygu; Sarayloo, Ehsan; Ulusu, Nuriye Nuray; PhD Student; Faculty Member; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); School of Medicine; N/A; N/A; 6807Metabolic syndrome, obesity and type 2 diabetes are metabolic disorders characterized by the insulin resistance and the impairment in the insulin secretion. Since impairment in the oxidative stress and adipocyte metabolism contribute to the formation of obesity and diabetes, targeting adipose tissue can be considered as an effective approach to fight against them. Rosiglitazone is used for treatment for patients with type 2 diabetes via inducing lipogenesis and transdifferentiation of white adipose tissue into brown adipose tissue. Since the development of such therapeutics is required to control the formation and function of brown fat cells, we aimed to reveal possible molecular mechanisms behind rosiglitazone induced biochemical changes in the adipose tissue. Cells were expanded in the adipocyte culture medium supplemented with 5 μg/mL insulin following 2 days' induction. After those cells were treated with rosiglitazone 0, 0.1 3 mol/L and 10 μmol/L rosiglitazone for 48 hours and at 8th day, cells were collected and stored at -80 °C. Then the cells were used to evaluate antioxidant enzyme activities, mineral and trace element levels and fatty acid composition. Glucose-6-phosphate dehydrogenase and glutathione reductase significantly reduced in rosiglitazone-treated groups compared to the control. Na, Mg, K, Ca, Cr, Fe, Ni, Cu, Zn, Rb, Sr, Cs, Ba and Pb were determined in the cell lysates via ICP-MS. Also, relative FAME content decreased in the rosiglitazone-treated groups compared to the control. Rosiglitazone treatment at low doses showed promising results which may promote brown adipose tissue formation.Publication Open Access The probabilistic serial mechanism with private endowments(Elsevier, 2010) Department of Economics; Yılmaz, Özgür; Faculty Member; Department of Economics; College of Administrative Sciences and Economics; 108638A random assignment is ordinally efficient if it is not stochastically dominated with respect to individual preferences over sure objects. When there are no private endowments, the set of ordinally efficient random assignments is characterized by the eating algorithm (Bogomolnaia and Moulin, 2001). When there are private endowments, the main requirement is individual rationality; however, the eating algorithm fails to deliver this property. Our contribution is the natural generalization of the eating algorithm for this general class of problems. The family of this generalized eating algorithm characterizes the set of individually rational and ordinally efficient random assignments. A special solution in this family, the individually rational probabilistic serial (PS(IR)), also achieves a new fairness axiom, no justified-envy. However, it is not immune to strategic manipulation. We show that individual rationality, no justified-envy and strategy-proofness are incompatible.Publication Open Access Outcomes of Norwood procedure with hypoplastic left heart syndrome: our 12-year single-center experience(Bayçınar Tıbbi Yayıncılık ve Reklam Hizmetleri, 2022) Özdemir, Fatih; Korun, Oktay; Dedemoğlu, Mehmet; Çiçek, Murat; Yurdakok, Okan; Altın, Hüsnü Fırat; Yılmaz, Emine Hekim; Yurtseven, Nurgül; Aydemir, Numan Ali; Sasmazel, Ahmet; Biçer, Mehmet; Koç University HospitalBackground: in this study, we aimed to analyze the predictors and risk factors of mortality in patients who underwent Norwood I procedure with the diagnosis of hypoplastic left heart syndrome. Methods: between January 2009 and December 2020, a total of 139 patients (95 males, 44 females) who underwent Norwood I procedure with the diagnosis of hypoplastic left heart syndrome in our center were retrospectively analyzed. Results: the median birth weight was 3,200 (range, 3,000 to 3,350) g and the median age at the time of operation was seven (range, 5 to 10) days. Pulmonary flow was achieved with a Sano shunt in the majority (72%) of patients. Survival rate was 41% after the first stage. Reoperation for bleeding (p=0.017), reoperation for residual lesion (p=0.011), and postoperative peak lactate level (p=0.029), were associated with in-hospital mortality. Nineteen (33%) of 57 patients died before the second stage. Thirty-three (58%) patients underwent second stage, and survival after the second stage was 94%. Thirteen patients underwent third stage, and survival after the third stage was 85%. Estimated probability of survival at six months, and one, two, three, and four years were 33%, 33%, 25%, 25%, and 22% respectively. Conclusion: hospital and inter-stage mortality rates are still high and this seems to be the most challenging period in term of survival efforts of the patients with hypoplastic left heart syndrome. Early recognition and reintervention of anatomical residual defects, close follow-up in the inter-stage period, and the accumulation of multidisciplinary experience may help to improve the results to acceptable limits. / Amaç: bu çalışmada, hipoplastik sol kalp sendromu tanısıyla Norwood I işlemi uygulanan hastalarda mortalitenin öngörücüleri ve risk faktörleri incelendi. Ça¬lış¬ma pla¬nı: Ocak 2009 ve Aralık 2020 tarihleri arasında merkezimizde hipoplastik sol kalp sendromu tanısıyla Norwood I işlemi uygulanan toplam 139 hasta (95 erkek, 44 kadın) retrospektif olarak incelendi. Bulgular: medyan doğum ağırlığı 3200 (dağılım, 3000-3350) g ve ameliyat sırasında medyan yaş yedi (dağılım, 5-10) gün idi. Hastaların büyük kısmında (%72) pulmoner akım, Sano şant ile sağlandı. İlk aşama sonrası sağkalım %41 idi. Kanama nedeniyle tekrar ameliyat (p=0.017), rezidü anatomik lezyon nedeniyle tekrar ameliyat (p=0.011) ve ameliyat sonrası birinci gün pik laktat seviyesi (p=0.029) hastane mortalitesi ile ilişkili idi. Taburcu edilen 57 hastanın 19’u (%33) ikinci aşamaya ulaşamadan kaybedildi. Otuz üç (%58) hastaya ikinci aşama ameliyatı uygulandı ve ikinci aşama sonrası sağkalım %94 idi. On üç hastaya üçüncü aşama ameliyatı uygulandı ve üçüncü aşama sonrası sağkalım %85 idi. Altı ay ve birinci, ikinci, üçüncü ve dördüncü yılda tahmini sağkalım olasılığı sırasıyla %33, %33, %25, %25 ve %22 idi. So¬nuç: hastane ve aşamalar arası mortalite oranları halen yüksek olup, hipoplastik sol kalp sendromu tanılı hastaların sağkalma çabalarındaki en zorlayıcı zaman dilimi olarak görünmektedir. Anatomik rezidü defektlerin erken tanılanması ve erken yeniden girişim yapılması, aşamalar arası dönemde yakın takip ve multidisipliner birikim ve tecrübe sonuçların kabul edilebilir seviyelere ulaşmasına yardım edebilir.Publication Open Access Predicting mortality in patients with spontaneous bacterial peritonitis using routine inflammatory and biochemical markers(Lippincott Williams and Wilkins (LWW), 2018) Iliaz, Raim; Özpolat, Tahsin; Demir, Kadir; Kaymakoğlu, Sabahattin; Beşışık, Fatih; Akyüz, Filiz; Baran, Bülent; Faculty Member; Koç University Hospital; 167583Objectives: Spontaneous bacterial peritonitis (SBP) is a common and high-mortality infectious complication of patients with cirrhosis. New inflammatory markers are associated with morbidity/mortality in various diseases. The aim of our study was to find the 30-day mortality rate of SBP and their predictors. Patients and methods: Seventy patients with cirrhosis complicated with SBP and 55 non-SBP controls were enrolled into the study, and patients were evaluated for mortality rate and its predictors. Results: The 30-day and 3-month mortality rates in the SBP group were 26.1 and 50.7%, respectively. Mortality rates were higher in the SBP group than in the controls. Symptoms at hospital admission and cell counts in ascitic fluid made no difference in predicting 30-day mortality. Patients with SBP with high serum neutrophil counts, high neutrophil-lymphocyte ratio, high C reactive protein (CRP)/albumin ratio, and high model for end-stage liver disease (MELD) score had higher 30-day mortality rates. We determined optimal cutoff values of MELD scores and serum neutrophil counts for predicting 30-day mortality as 20.5 and 6850/mm(3), respectively. The sensitivity and specificity for the MELD cutoff value were 83.3 and 80.4%, respectively. We also followed up patients for 60 months after SBP; the patients with high inflammatory markers and MELD scores at the time of SBP diagnosis had worse survival compared with the group with lower levels. Conclusion: Our results suggest that SBP has high 30-day mortality. MELD scores and inflammatory markers (CRP, CRP albumin ratio, neutrophil-lymphocyte ratio) may be used to predict mortality in patients with SBP.Publication Open Access Long-term prognosis of commercially sexually exploited youth in Turkey: brief report(Anadolu Psikiyatri Dergisi - Anatolian Journal of Psychiatry, 2017) Semerci, B.; Tufan, A. E.; Sanli, I.; N/A; Taşkıran, Ali Sarper; Other; School of Medicine; 195168Objective: Factors contribute to commercial sexual exploitation of youth (CSEY) and a variety of physical and psychological consequences of CSEY were previously discussed in the literature. The aim of the current study was to determine the long term prognosis of a sample of CSEY in Turkey. Methods: A sample of 108 CSEY (all females) with a mean age of 16.7 +/- 2.7 (range: 9-22) years living in a specialized center for protection against perpetrators were examined in terms of their sociodemographic variables, previous abuse history, family history and current psychopathology. Identified cases were referred for psychiatric evaluation. We obtained follow-up data 11 years after initial contact from this cohort (mean age 25.9 +/- 2.6 at time of follow-up) with the subjects and received information regarding their current functioning. Results: Follow up data revealed that recommendations during psychiatric follow up could not be acted upon. 71.4% of the initial sample (n= 76) could be reached via direct or indirect contacts. We found that good/superior functioning was very rare and that one-third of the sample that could be reached still was being sexually exploited. Important considerations derived from the results were discussed in the current article.