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Master Thesis Hipotalamus-hipofiz-adrenal Ekseninin Doğrusal Olmayan Denetimi(2019) Mohsın, Ahmed Hefdhı Mohsın; Doruk, Reşat ÖzgürBu tez çalışmasında canlıların sirkadyen ritm ve immünolojik strese verilen fizyolojik yanıt mekanizmasında önemli rol oynayan hipotalamus-hipofiz-adrenal ekseninin otomatik denetimine ilişkin bir çalışma sunulmaktadır. Hipotalamus-hipofiz-adrenal ekseninin matematiksel modeli doğrusal olmayan türevsel denklemlerden meydana gelmektedir. Bu nedenle geri adımlamalı ve geri beslemeye dayalı doğrusallaştırma olarak bilinen doğrusal olmayan denetim yöntemleri tercih edilmektedir. Denetim mekanizmasında girdi adrenokortikotropin enjeksiyonu olup, denetimde aynı hormonunun ve kortizolün plazma derişim düzeyleri ölçülerek işlem yapılmaktadır. Kortizolün günlük ritmini koruyabilmek için yukarıda bahsedilen denetleyiciler adrenokortikotropin hormonunun enjeksiyonunu ayarlamak suretiyle kortizolün belirlenen periyodik sinüzoidal bir ritmi takip etmesini sağlar. İlk yapılan benzetimlerde negatif değerli derişimler görüldüğünden denetim kazançlarının değiştirilmesi gerekli olmuştur. Bu işlemleri yaparken geri adımlamalı ve geri beslemeye dayalıu doğrusallaştırmaya dayalı denetim süreçlerinde kazançlar ayrı ayrı ayarlanmak durumunda kalınmıştır. Sonuçlar göstermektedir ki, gerek geri beslemeye dayalı doğrusallaştırma gerekse de ger adımlamalı denetimlerde kazançları uygun şekilde seçmek kaydıyla iyi performans elde edilmiştir. Kazançları seçerken öncelikli olarak negatif değerli derişimlerin oluşmamasına dikkat edilmiştir. Bunun yanı sıra derişim profilinde titreşim oluşmamasına da özen gösterilmiştir. Anahtar Kelimeler: Hipotalamus-Hipofiz-Adrenal ekseni, homeostazi, sirkadyen ritmler, geri adımlamalı denetim, geri beslemeye dayalı doğrusallaştırma.Article Citation - WoS: 33Social Jetlag Is Associated With the Frequency of Consumption of Sugar-Sweetened Beverages and a High Bmi Percentile in Adolescents: Results of the Cross-Sectional Family Life, Activity, Sun, Health, and Eating (flashe) Study(Elsevier Science inc, 2021) Cetiner, Ozlem; Yildirim, Gonca; Kalyoncu, Zeynep BegumBackground Social jetlag (SJL) occurs in adolescents due to misalignment of the bio-logical and social clocks, so that most teens wake up earlier than their biological clocks on weekdays and delay bedtime and wake up time on weekends. This shift in sleep timing among adolescents is associated with an adverse endocrine and behavioral risk profile, in addition to increased food consumption and increased body mass index (BMI). Objective The aim of this study was to determine the association between SJL, and the frequency of consumption of multiple food and beverage groups and BMI percentile in adolescents. Design Publicly available data from the cross-sectional Family Life, Activity, Sun, Health, and Eating (FLASHE) study were analyzed. Participants Participants from the FLASHE study were recruited from all regions of the United States between April and October 2014. Among the 1,581 adolescents aged 12 through 17 years in the original study, 1,556 with complete sleep data were analyzed. Main outcome measures The difference between the frequency of dietary consump-tion according to the Dietary Screener Questionnaire and BMI percentile was assessed in adolescents grouped according to SJL, as follows: no SJL: less than 1-hour difference; mild SJL: 1-to 2-hour difference; and severe SJL: more than 2-hour difference. Statistical analyses performed Differences in the frequency of food consumption were analyzed using the Kruskal-Wallis test. Secondary outcomes were analyzed using logistic regression models. Results Daily consumption frequency of sugar-sweetened beverages and fruits and vegetables differed among the 3 groups. Likewise, the BMI percentile differed among the 3 groups and was highest in the severe SJL group. Those in the severe SJL group had a 1.84-fold higher probability of having overweight or obesity (95% CI 1.83 to 1.84) than those in the no SJL group. Conclusions Severe SJL is associated with a higher frequency of sugar-sweetened beverage consumption and higher odds of having overweight or obesity compared with no SJL in adolescents. J Acad Nutr Diet. 2021;121(9):1721-1731.Article Automatic Control of Hypothalamus-Pituitary Axis Dynamics(Elsevier Ireland Ltd, 2019) Doruk, R. Ozgur; Mohsin, Ahmed H.Background and Objective: In this study, a presentation is made for the automatic control of the hypothalamus-pituitary-adrenal axis which plays an important role in the immune stress responses and the circadian rhythms of mammalian organisms. Methods: Control approaches are implemented on a novel second order nonlinear system which accepts adrenocorticotropin hormone as an input and models the variation of plasma concentrations of adrenocorticotropin and cortisol respectively. The control methods are based on back-stepping and input-output feedback linearization techniques. The controllers adjust the adrenocorticotropin injection to maintain the daily rhythm of the cortisol concentration. In accordance with the periodicity of biological clock mechanism, we provide a sinusoidally varying cortisol reference to the controllers. Results: Numerical simulations are performed (on MATLAB) to demonstrate the closed loop performance of the controllers. Major concerns in the selection of the control gains are chattering and negative concentration in responses. The simulation results showed that one can successfully find gain levels which do not lead to those issues. However, the gains lie in different ranges for back-stepping and feedback linearization based controllers. Conclusion: The results showed that, both back-stepping and feedback linearization based controllers fulfilled their duty of synchronization of the cortisol concentration to a reference daily periodic rhythm. In addition to that, the risk of negative valued adrenocorticotropin injection can be eliminated by properly choosing the controller gains. (C) 2019 Elsevier B.V. All rights reserved.
