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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 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 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 Mid-term results of open debridement and reattachment surgery for insertional Achilles tendinopathy: a retrospective clinical study(Aves, 2020) Yontar, Necip Selçuk; Can, Ata; Öğüt, Tahir; Aslan, Lercan; Faculty Member; Koç University HospitalObjective: the aim of this study was to determine the effects of age and body mass index (BMI) on the functional outcomes, satisfaction rates, and recovery time after open debridement and reattachment surgery in non-athletic patients with insertional Achilles tendinopathy (IAT). Methods: in this retrospective study, 33 non-athletic patients (34 ankles) in whom open debridement and reattachment surgery was performed for IAT from 2006 to 2016 were included. Change in pain intensity was assessed using a Visual Analogue Scale (VAS) preoperatively and at the final follow-up. Functional assessment was done by preoperative and postoperative American Orthopaedics Foot and Ankle Score (AOFAS) and final follow-up Victorian Institute of Sport Tendon Study Group-Achilles Tendinopathy score (VISA-A). Patient satisfaction was evaluated by Roles - Maudsley score (RMS). The recovery time was defined as the time interval from the first appearance to postoperative relief of symptoms and recording. In addition, the recurrent Haglund's deformity was determined by postoperative control radiographs. Results: the mean age at the time of the operation was 51.19 years. The mean follow-up was 61.75 +/- 8.49 months. According to BMI, 5 patients were determined as morbid obese, 19 as obese, 3 as overweight, and 6 as normal. The mean VAS score significantly decreased from 8.5 preoperatively to 1.3 postoperatively (p<0.001). The mean AOFAS score significantly improved from 55.8 preoperatively to 92 postoperatively (p<0.001). Postoperative VISA-A score was 86% (range=32%-100%). According to RMS, 22 patients reported the result as excellent, 8 as good, 2 as fair, and 1 as poor. The mean recovery time was 11.8 (range=2-60) months, but one patient did not reach a symptom free status and thus was not included in the recovery time analysis. Postoperative control radiographs revealed signs of recurrence deformity in four patients. Recovery time showed a negative correlation with the age of the patients (r=-0.65). Postoperative scores and BMI showed no significant correlations with the recovery time on the basis of Spearman's rho test (p=0.196). Conclusion: the results of this study have shown that open debridement and reattachment surgery may be an effective surgical method in relieving pain and improving functional status with high satisfaction rate and acceptable recovery time in the management of non-athletic patients with IAT.Publication Open Access Minimal number of singular fibers in a nonorientable Lefschetz fibration(Springer, 2022) Onaran, Sinem; Department of Mathematics; Özbağcı, Burak; Faculty Member; Department of Mathematics; College of Sciences; 29746We show that there exists an admissible nonorientable genus g Lefschetz fibration with only one singular fiber over a closed orientable surface of genus h if and only if g >= 4 and h >= 1.Publication Open Access Chitosan channels stuffed with mesenchyme originated stem/progenitor cells for renovate axonal regeneration in complete spinal cord transection(Turkish Neurosurgical Society, 2021) Çakıcı, Nazlı; Bozkurt, Gökhan; Puralı, Nuhan; Denkbaş, Emir Baki; Korkusuz, Petek; Uçkan Çetinkaya, Duygu; Başak, Ahmet Tulgar; Doctor; Koç University HospitalAim: to examine the implantation of chitosan channels stuffed with mesenchyme-originated stem/progenitor cells (MSPCs) derived from adult rats in a spinal cord transection model. The level of axonal regeneration, the effect of chitosan channels on the survival of MSPCs, and the functional recovery results were also evaluated. Material and methods: chitosan channels stuffed with MSPCs were implanted at the level of T8 in a transected rat spinal cord. MSPCs were harvested from the pelvic bone marrow of adult rats, and the MSPC-chitosan channel group was compared with three control groups. The axonal regeneration capacity, the effect of chitosan channels on the survival of MSPCs, and the functional recovery results were compared among four groups. The survival of MSPCs was evaluated using histopathological techniques and electron microscopy, axonal regeneration/germination was evaluated by confocal microscopy, and locomotor function was assessed for 4 weeks using the Basso, Beattie, and Bresnahan locomotor score. Results: the MSPC-chitosan channel group exhibited enhanced survival of transplanted MSPCs compared with MSPCs transplanted directly into the lesion cavity, although no significant difference was detected in locomotor function between the treatment and control groups. The MSPC-chitosan channel group demonstrated thicker myelination of axons than the other groups. Conclusion: chitosan channels promoted the survival of transplanted MSPCs and created a tissue bridge after complete spinal cord transection. They also induced axonal regeneration and germination. No significant improvement in functional recovery was found between the groups.Publication Open Access Emotion regulation function of autobiographical remembering(Turkish Psychologists Association / Türk Psikologlar Derneği, 2020) Öner, Sezin; Department of Psychology; Gülgöz, Sami; Faculty Member; Department of Psychology; College of Social Sciences and Humanities; 49200In this study, we aimed to investigate emotion regulation function of autobiograhical remembering within an integrative perspective. We asked participants to recall sadness, anger and happiness related events for emotion induction, then they recalled any random memory that came to their mind. In the latter remembering experience. Pre- and post-report emotionality ratings and phenomenological features of the recall were examined to test whether subsequent recall served to upregulate positive emotions. Only in sadness and anger memory groups who recalled memories with high emotional impact reported more positive emotions after subsequent remembering. Also, we found distinct mechanisms by which sadness and anger groups used for emotion regulation such that for the sadness group whereas the emotional intensity accounted for the role of upregulation, for the anger group, importance of the event predicted enhanced positivity. Findings are discussed in the context of the emotion regulation function of autobiographical remembering. / Bellek ve duygusal süreçlerin ilişkisi alanyazında geniş yer tutmaktadır. Bu iki kavramı bütünsel bir bakışla incelemeyi amaçladığımız bu çalışmada otobiyografik belleğin duygu düzenleme işlevine odaklanılmıştır. Üç ayrı gruptaki katılımcılara, üzüntü, öfke veya mutluluk uyandıracak anılar hatırlatılmış ardından da bir yönerge verilmeden herhangi bir anı hatırlamaları istenmiştir. Katılımcılar ayrıca anı özelliklerini belirtmişler ve duygu düzenleme stratejilerini değerlendirmişlerdir. Hatırlamadan önce ve sonra katılımcıların nasıl hissettikleri de sorulmuştur. Bulgulara bakıldığında, duygusal etkisi yüksek anı hatırlayan olumsuz anı grubu katılımcılarının, yönergesiz hatırlama sonrasında duygu durumlarını belirgin olarak olumlulaştırdığı görülürken, bu değişimin üzüntü ve öfke gruplarında farklı anı özellikleri tarafından yürütüldüğünü saptanmıştır. Üzüntü grubunda yönergesiz anının duygusal yoğunluğunun, öfke grubunda ise anının öneminin duygu değişimine aracı olduğu gösterilmiştir. Bulgular, otobiyografik hatırlamanın duygu düzenleme işlevi bağlamında tartışılacaktır.Publication Open Access Tissue thiol concentration in high-grade gliomas: is there any association between IDH1 mutation presence and tumoral cellular antioxidant defense?(Turkish Neurosurgical Society, 2021) Evran, Şevket; Kayhan, Ahmet; Çevik, Serdar; Katar, Salim; Kaya, Mustafa; Sönmez, Derya; Serin, Huriye; Hanımoğlu, Hakan; Kaynar, Mehmet Yaşar; Baran, Oğuz; Faculty Member; Koç University HospitalAim: to assess and compare the antioxidant capacities of high-grade gliomas (HGG) according to their grades and the presence of isocitrate dehydrogenase 1 (IDH1) mutation using tissue thiol level measurement. Material and methods: tissue thiol concentrations were measured in 41 HGG samples and 21 healthy brain tissues obtained from autopsy procedures, which were performed within the first 4 hours of death. All samples were stored at -80 degrees C, and a thiol quantification kit was used in evaluating tissue thiol levels. The Number Cruncher Statistical System was used for statistical analyses to detect the differences between the control group and the HGG group, which was also divided into subgroups according to their grade and IDH1 mutation presence. Results: the tissue thiol levels of HGGs were found to be higher than the control group (p=0.001). Although the median thiol levels of Grade 4 gliomas were higher than those of Grade 3, no statistically significant difference was noted (p=0.076). When all tumors were compared according to the IDH1 mutation presence, IDH1-negative (IDH1-) HGGs had higher thiol contents than IDH1 mutant (IDH1+) HGGs (p=0.001). The thiol levels of Grade 4 IDH1- gliomas were statistically significantly higher than of Grade 3 gliomas (p=0.023), but no statistically significant difference between the thiol levels of Grade 3 and Grade 4 IDH1+ tumors was noted (p=0.459). Conclusion: we have demonstrated the higher thiol concentrations of HGGs, particularly IDH1- ones. The sulfhydryl contents of gliomas as an indicator of tumoral antioxidant capacity may be responsible for the treatment resistance of IDH1- gliomas, the mechanism of which is not clear. Thiols can be a novel target for treatment, considering the unsatisfactory results of current modalities for HGGs.Publication Open Access Recommendations for hepatitis B immunoglobulin and antiviral prophylaxis against hepatitis B recurrence after liver transplantation(Aves, 2021) Akarsu, Mesut; Önem, Soner; Turan, İlker; Adalı, Gupse; Akdoğan, Meral; Aladağ, Murat; Balaban, Yasemin; Danış, Nilay; Dayangaç, Murat; Gökcan, Hale; Sertesen, Elif; Gürakar, Merve; Harputluoğlu, Murat; Kabacam, Gökhan; Karademir, Sedat; Kıyıcı, Murat; İdilman, Ramazan; Karasu, Zeki; Akyıldız, Murat; Gençdal, Genco; Faculty Member; Doctor; School of Medicine; Koç University Hospital; 123080; N/AThe combination of hepatitis B immunoglobulin and potent nucleos(t)ide analogs after liver transplantation is considered as the standard of care for prophylaxis against hepatitis B virus recurrence. However, the recommended doses, route of administration, and duration of HBIG administration remain unclear. Moreover, hepatitis B immunoglobulin-free prophylaxis with potent nucleos(t)ide analogs has shown promising disease outcomes in preventing hepatitis B virus recurrence. The current recommendations, produced by the Turkish Association for the Study of the Liver, Acute Liver Failure and Liver Transplantation Special Interest Group, suggest a reduced need for hepatitis B immunoglobulin administration with effective long-term suppression of hepatitis B virus replication using potent nucleos(t)ide analogs after liver transplantation.Publication Open Access Commentary: challenges for PhD students during COVID-19 pandemic: turning crisis into an opportunity(Wiley, 2020) Aydemir, Duygu; 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; 6807COVID-19 results in the suspension of life all over the world. Universities suspended their academic activities except for online courses for undergrad and grad students. However, PhD students in both biochemistry and molecular biology fields must hold their experiments at the laboratories. Even under these extreme circumstances, the academic journey of a master's or PhD student should not be stopped; on contrary, they need to use these times to improve their knowledge related to their fields. Therefore, they can turn this COVID-19 crisis into an opportunity for themselves.