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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Comparative spectroscopic investigation of Tm3+: tellurite glasses for 2-mu m lasing applications(Multidisciplinary Digital Publishing Institute (MDPI), 2018) Kurt, Adnan; Speghini, Adolfo; Bettinelli, Marco; Department of Electrical and Electronics Engineering; Department of Physics; Department of Electrical and Electronics Engineering; Department of Physics; Çankaya, Hüseyin; Görgülü, Adil Tolga; Sennaroğlu, Alphan; Researcher; Master Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; College of Sciences; N/A; N/A; 23851We performed a comparative spectroscopic analysis on three novel Tm3+: tellurite-based glasses with the following compositions Tm2O3: TeO2-ZnO (TeZnTm), Tm2O3: TeO2-Nb2O5 (TeNbTm), and Tm3+: TeO2-K2O-Nb2O5 (TeNbKTm), primarily for 2-mu m laser applications. Tellurite glasses were prepared at different doping concentrations in order to investigate the effect of Tm3+ ion concentration as well as host composition on the stimulated emission cross sections and the luminescence quantum efficiencies. By performing Judd-Ofelt analysis, we determined the average radiative lifetimes of the H-3(4) level to be 2.55 +/- 0.07 ms, 2.76 +/- 0.03 ms and 2.57 +/- 0.20 ms for the TeZnTm, TeNbTm and TeNbKTm samples, respectively. We clearly observed the effect of the cross-relaxation, which becomes significant at higher Tm2O3 concentrations, leading to the quenching of 1460-nm emission and enhancement of 1860-nm emission. Furthermore, with increasing Tm2O3 concentrations, we observed a decrease in the fluorescence lifetimes as a result of the onset of non-radiative decay. For the H-3(4) level, the highest obtained quantum efficiency was 32% for the samples with the lowest Tm2O3 ion concentration. For the 1860-nm emission band, the average emission cross section was determined to measure around 6.33 +/- 0.34 x 10(-21) cm(2), revealing the potential of thulium-doped tellurite gain media for 2-mu m laser applications in bulk and fiber configurations.Publication Open Access Increased hemoglobin oxygen affinity with 5-hydroxymethylfurfural supports cardiac function during severe hypoxia(Frontiers, 2019) Lucas, Alfredo; Ao-ieong, Eilleen S. Y.; Williams, Alexander T.; Jani, Vivek P.; Muller, Cynthia R; Cabrales, Pedro; N/A; Yalçın, Özlem; Researcher; School of Medicine; 218440Acclimatization to hypoxia or high altitude involves physiological adaptation processes, to influence oxygen (O2) transport and utilization. Several natural products, including aromatic aldehydes and isothiocyanates stabilize the R-state of hemoglobin (Hb), increasing Hb-O2 affinity and Hb-O2 saturation. These products are a counter intuitive therapeutic strategy to increase O2 delivery during hypoxia. 5-Hydroxymethylfurfural (5-HMF) is well known Amadori compound formed during the Maillard reaction (the non-enzymatic browning and caramelization of carbohydrate-containing foods after thermal treatment), with well documented effects in Hb-O2 affinity. This study explores the therapeutic potential of 5-HMF on left ventricular (LV) cardiac function (LVCF) during hypoxia. Anesthetized Golden Syrian hamsters received 5-HMF i.v., at 100 mg/kg and were subjected to stepwise increased hypoxia (15, 10, and 5%) every 30 min. LVCF was assessed using a closed chest method with a miniaturized conductance catheter via continuous LV pressure-volume (PV) measurements. Heart hypoxic areas were studied using pimonidazole staining. 5-HMF improved cardiac indices, including stroke volume (SV), cardiac output (CO), ejection fraction (EF), and stroke work (SW) compared to the vehicle group. At 5% O2, SV, CO, EF, and SW were increased by 53, 42, 33, and 51% with 5-HMF relative to vehicle. Heart chronotropic activity was not statistically changed, suggesting that differences in LV-CF during hypoxia by 5-HMF were driven by volume dependent effects. Analysis of coronary blood flow and cardiac muscle metabolism suggest no direct pharmacological effects from 5-HMF, therefore these results can be attributed to 5-HMF-dependent increase in Hb-O2 affinity. These studies establish that naturally occurring aromatic aldehydes, such as 5-HMF, produce modification of hemoglobin oxygen affinity with promising therapeutic potential to increase O2 delivery during hypoxic hypoxia.Publication Open Access Fear of happiness among college students: the role of gender, childhood psychological trauma, and dissociation(Medknow Publications, 2019) Türk, Tuğba; Öztürk, Erdinç; N/A; Şar, Vedat; Faculty Member; School of Medicine; 8542Aims: this study aimed to evaluate the fear of happiness among college students and its relationship to gender, childhood psychological trauma, and dissociation. Setting and Design: College students were addressed as study population, and a relational screening method was implemented. Materials and Methods: among 184 participants, 93 (50.5%) were women. The Fear of Happiness Scale (FHS), the Childhood Trauma Questionnaire (CTQ), and the Dissociative Experiences Scale (DES) were administered to all participants. Statistical Analysis Used: MannuWhitney-U and Student's t-tests were implemented for comparison of groups. Pearson correlation and stepwise multiple regression analyses were conducted to identify associations between variables. Results: there were no differences on DES, FHS, and CTQ total scores between genders. DES was associated with CTQ total scores in both genders. Women had higher scores than men on childhood emotional abuse and fear of "cheerfulness ends up with bad faith." Compared to nonmembers, female dissociative taxon members had higher scores on all childhood trauma types except sexual abuse, and on all types of fear of happiness except "good fortune ends up with disaster" which was the only type of fear significantly elevated among male dissociative taxon members. A stepwise regression analysis revealed that depersonalization, childhood emotional neglect, and physical abuse predicted fear of happiness among women which was predicted by absorption among men. Conclusions: there is a relationship between childhood psychological trauma, dissociation, and fear of happiness. Women seem to be more vulnerable in this path of obsessional thinking which affects different realms in male and female genders.Publication Open Access The after-hours circadian mutant has reduced phenotypic plasticity in behaviors at multiple timescales and in sleep homeostasis(Nature Publishing Group (NPG), 2017) Maggi, Silvia; Balzani, Edoardo; Lassi, Glenda; Garcia-Garcia, Celina; Plano, Andrea; Espinoza, Stefano; Mus, Liudmila; Tinarelli, Federico; Nolan, Patrick M.; Gainetdinov, Raul R.; Nieus, Thierry; Tucci, Valter; Department of Psychology; Department of Psychology; Balcı, Fuat; Faculty Member; College of Social Sciences and Humanities; 51269Circadian clock is known to adapt to environmental changes and can significantly influence cognitive and physiological functions. In this work, we report specific behavioral, cognitive, and sleep homeostatic defects in the after hours (Afh) circadian mouse mutant, which is characterized by lengthened circadian period. We found that the circadian timing irregularities in Afh mice resulted in higher interval timing uncertainty and suboptimal decisions due to incapability of processing probabilities. Our phenotypic observations further suggested that Afh mutants failed to exhibit the necessary phenotypic plasticity for adapting to temporal changes at multiple time scales (seconds-to-minutes to circadian). These behavioral effects of Afh mutation were complemented by the specific disruption of the Per/Cry circadian regulatory complex in brain regions that govern food anticipatory behaviors, sleep, and timing. We derive statistical predictions, which indicate that circadian clock and sleep are complementary processes in controlling behavioral/cognitive performance during 24 hrs. The results of this study have pivotal implications for understanding how the circadian clock modulates sleep and behavior.Publication Open Access Al2O3 micro- and nanostructures affect vascular cell response(Royal Society of Chemistry (RSC), 2016) Kiefer, Karin; Akpınar, Gürler; Haidar, Ayman; Ikier, Tuba; Akkan, Çağrı Kaan; Akman, Erhan; Lee, Juseok; Miro, Marina Martinez; Kaçar, Elif; Demir, Arif; Veith, Michael; Kasap, Murat; Kesmez, Mehmet; Abdul-Khaliq, Hashim; Aktaş, Cenk; N/A; Ural, Dilek; Faculty Member; School of Medicine; 1057In-stent restenosis (ISR) is one of the most common and serious complications observed after stent implantation. ISR is characterized by the inordinate proliferation of smooth muscle cells (SMC) that leads to narrowing of the blood vessels. To achieve a healthy endothelium, it is critical to selectively enhance the growth of endothelial cells (EC) while suppressing the growth of smooth muscle cells, which is still a major challenge and yet to be achieved. In this study, novel surfaces have been developed to support the selective growth of endothelial cells. Micro-and nanostructured Al2O3 surfaces with unique topographical features were fabricated and tested. Surface characterization and cellular response of endothelial cells (HUVEC) as well as smooth muscle cells (HUVSMC) has been investigated at cellular and molecular levels. A topography driven selective cell response of ECs over SMCs was demonstrated successfully. This selective response of ECs was also analyzed at protein levels in order to understand the basic mechanism.Publication Open Access Improved superconducting properties in the Mg11B2 low activation superconductor prepared by low-temperature sintering(Nature Publishing Group (NPG), 2016) F. Cheng, Y.; Liu, Z. Ma; Hossain, M. S.; Department of Chemistry; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; College of Sciences; 178882Mg11B2 has a great application prospect in the superconducting coils for fusion reactor as the “low activation superconductors”. The un-doped Mg11B2 and Cu-doped Mg11B2 bulks using 11B as a boron precursor were fabricated by low-temperature sintering in present work. It was found that the prepared Mg11B2 low activation superconductors exhibit better Jc performance than all of other Mg11B2 samples reported in previous studies. As for Cu doped Mg11B2, minor Cu addition can obviously improve the Mg11B2 grain crystallization and reduce the amount of MgO impurity. Hence, improved grain connectivity and higher Jc at low fields is obtained in Cu doped Mg11B2 samples. For un-doped samples, refined grains and more MgO impurity with proper size brought about more flux pinning centers, resulting in better Jc performance at high fields.Publication Open Access Chaotic spin correlations in frustrated Ising hierarchical lattices(American Physical Society (APS), 2009) Berker, A. Nihat; Department of Physics; Department of Physics; Aral, Neşe; College of SciencesSpin-spin correlations are calculated in frustrated hierarchical Ising models that exhibit chaotic renormalization-group behavior. The spin-spin correlations, as a function of distance, behave chaotically. The far correlations, but not the near correlations, are sensitive to small changes in temperature or frustration, with temperature changes having a larger effect. On the other hand, the calculated free energy, internal energy, and entropy are smooth functions of temperature. The recursion-matrix calculation of thermodynamic densities in a chaotic band is demonstrated. The leading Lyapunov exponents are calculated as a function of frustration.Publication Open Access Youth with chronic health problems: how do they fare in main-stream mentoring programs?(BioMed Central, 2018) Lipman, Ellen L.; Dewit, David; DuBois, David L.; Larose, Simon; Department of Psychology; Department of Psychology; Gürel, Gizem Erdem; Faculty Member; College of Social Sciences and Humanities; 222027Background: Youth with chronic physical health problems often experience social and emotional problems. We investigate the relationship between participation in the Big Brothers Big Sisters of Canada community-based mentoring programs (BBBS) and youth social and mood outcomes by youth health status. Methods: Youth newly enrolled in BBBS were classified by health status (one or more chronic physical health problems without activity limitation, n = 191; one or more chronic physical health problems with activity limitation, n = 94; no chronic health problem or activity limitation, n = 536) and mentoring status (yes/no) at 18 month follow-up. Youth outcomes measured at follow-up were social anxiety, depressed mood, and peer self-esteem. Results: Youth with chronic health problems and activity limitation were more likely to live with two biological parents, use mental health or social services, and have parents who reported difficulties with depressed mood, social anxiety, family functioning and neighbourhood problems. At 18 month follow-up, mentored youth in this health status group experienced fewer symptoms of social anxiety and higher peer self-esteem compared to non-mentored youth. Mentored youth with chronic health problems without activity limitation andmentored youth with no health problems or limitations did not show significant improvements in social anxiety and peer self-esteem. Regardless of their health status, mentored youth reported fewer symptoms of depressed mood than non-mentored youth. Conclusions: Youth with chronic health problems, particularly those with activity limitation as well, demonstrate a capacity to experience social and mood benefits associated with mentoring.Publication Open Access Transcriptomic response of yeast cells to ATX1 deletion under different copper levels(BioMed Central, 2016) Cankorur-Çetinkaya, Ayça; Eraslan, Serpil; Kırdar, Betül; Eraslan, Serpil; Other; Koç University HospitalBackground: Iron and copper homeostatic pathways are tightly linked since copper is required as a cofactor for high affinity iron transport. Atx1p plays an important role in the intracellular copper transport as a copper chaperone transferring copper from the transporters to Ccc2p for its subsequent insertion into Fet3p, which is required for high affinity iron transport. Results: In this study, genome-wide transcriptional landscape of ATX1 deletants grown in media either lacking copper or having excess copper was investigated. ATX1 deletants were allowed to recover full respiratory capacity in the presence of excess copper in growth environment. The present study revealed that iron ion homeostasis was not significantly affected by the absence of ATX1 either at the transcriptional or metabolic levels, suggesting other possible roles for Atx1p in addition to its function as a chaperone in copper-dependent iron absorption. The analysis of the transcriptomic response of atx1 Delta/atx1 Delta and its integration with the genetic interaction network highlighted for the first time, the possible role of ATX1 in cell cycle regulation, likewise its mammalian counterpart ATOX1, which was reported to play an important role in the copper-stimulated proliferation of non-small lung cancer cells. Conclusions: The present finding revealed the dispensability of Atx1p for the transfer of copper ions to Ccc2p and highlighted its possible role in the cell cycle regulation. The results also showed the potential of Saccharomyces cerevisiae as a model organism in studying the capacity of ATOX1 as a therapeutic target for lung cancer therapy.Publication Open Access The relationship between co-speech gesture production and macrolinguistic discourse abilities in people with focal brain injury(Elsevier, 2018) Chatterjee, Anjan; Department of Psychology; Department of Psychology; Akbıyık, Seda; Karaduman, Ayşenur; Göksun, Tilbe; Master Student; Faculty Member; College of Social Sciences and Humanities; N/A; N/A; 47278Brain damage is associated with linguistic deficits and might alter co-speech gesture production. Gesture production after focal brain injury has been mainly investigated with respect to intrasentential rather than discourse-level linguistic processing. In this study, we examined 1) spontaneous gesture production patterns of people with left hemisphere damage (LHD) or right hemisphere damage (RHD) in a narrative setting, 2) the neural structures associated with deviations in spontaneous gesture production in these groups, and 3) the relationship between spontaneous gesture production and discourse level linguistic processes (narrative complexity and evaluation competence). Individuals with LHD or RHD (17 people in each group) and neurotypical controls (n = 13) narrated a story from a picture book. Results showed that increase in gesture production for LHD individuals was associated with less complex narratives and lesions of individuals who produced more gestures than neurotypical individuals overlapped in frontal-temporal structures and basal ganglia. Co-speech gesture production of RHD individuals positively correlated with their evaluation competence in narrative. Lesions of RHD individuals who produced more gestures overlapped in the superior temporal gyrus and the inferior parietal lobule. Overall, LHD individuals produced more gestures than neurotypical individuals. The groups did not differ in their use of different gesture forms except that LHD individuals produced more deictic gestures per utterance than RHD individuals and controls. Our findings are consistent with the hypothesis that co-speech gesture production interacts with macro-linguistic levels of discourse and this interaction is affected by the hemispheric lateralization of discourse abilities.