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33 results on '"Yıldız, Sercan"'

1. alfonso: Matlab package for nonsymmetric conic optimization

Author

Papp, Dávid and Yıldız, Sercan

Subjects
Mathematics - Optimization and Control, 90C25, 90-04, 65K05, 90C51, 90C22
Abstract

We present alfonso, an open-source Matlab package for solving conic optimization problems over nonsymmetric convex cones. The implementation is based on the authors' corrected analysis of a primal-dual interior-point method of Skajaa and Ye. This method enables optimization over any convex cone as long as a logarithmically homogeneous self-concordant barrier is available for the cone or its dual. This includes many nonsymmetric cones, for example, hyperbolicity cones and their duals (such as sum-of-squares cones), semidefinite and second-order cone representable cones, power cones, and the exponential cone. Besides enabling the solution of problems which cannot be cast as optimization problems over a symmetric cone, it also offers performance advantages for problems whose symmetric cone programming representation requires a large number of auxiliary variables or has a special structure that can be exploited in the barrier computation. The worst-case iteration complexity of alfonso is the best known for non-symmetric cone optimization: $O(\sqrt{\nu}\log(1/\epsilon))$ iterations to reach an $\epsilon$-optimal solution, where $\nu$ is the barrier parameter of the barrier function used in the optimization. alfonso can be interfaced with a Matlab function (supplied by the user) that computes the Hessian of a barrier function for the cone. For convenience, a simplified interface is also available to optimize over the direct product of cones for which a barrier function has already been built into the software. This interface can be easily extended to include new cones. Both interfaces are illustrated by solving linear programs. The oracle interface and the efficiency of alfonso are also demonstrated using a design of experiments problem in which the tailored barrier computation greatly decreases the solution time compared to using state-of-the-art conic optimization software., Comment: This is an early but essentially complete preprint submitted to the INFORMS Journal on Computing on August 19, 2020. The revised and final version of this paper will appear there. The accompanying software can be downloaded from https://github.com/dpapp-github/alfonso

Published
2021
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3. Optimization of spatiotemporally fractionated radiotherapy treatments with bounds on the achievable benefit

Author

Gaddy, Melissa R., Yıldız, Sercan, Unkelbach, Jan, and Papp, Dávid

Subjects
Physics - Medical Physics, 92C50, 90C22, 90C26, 90C90
Abstract

Spatiotemporal fractionation schemes, that is, treatments delivering different dose distributions in different fractions, may lower treatment side effects without compromising tumor control. This is achieved by hypofractionating parts of the tumor while delivering approximately uniformly fractionated doses to the healthy tissue. Optimization of such treatments is based on biologically effective dose (BED), which leads to computationally challenging nonconvex optimization problems. Current optimization methods yield only locally optimal plans, and it has been unclear whether these are close to the global optimum. We present an optimization model to compute rigorous bounds on the normal tissue BED reduction achievable by such plans. The approach is demonstrated on liver tumors, where the primary goal is to reduce mean liver BED without compromising other treatment objectives. First a uniformly fractionated reference plan is computed using convex optimization. Then a nonconvex quadratically constrained quadratic programming model is solved to local optimality to compute a spatiotemporally fractionated plan that minimizes mean liver BED subject to the constraints that the plan is no worse than the reference plan with respect to all other planning goals. Finally, we derive a convex relaxation of the second model in the form of a semidefinite programming problem, which provides a lower bound on the lowest achievable mean liver BED. The method is presented on 5 cases with distinct geometries. The computed spatiotemporal plans achieve 12-35% mean liver BED reduction over the reference plans, which corresponds to 79-97% of the gap between the reference mean liver BEDs and our lower bounds. This indicates that spatiotemporal treatments can achieve substantial reduction in normal tissue BED, and that local optimization provides plans that are close to realizing the maximum potential benefit.

Published
2017
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4. Sum-of-squares optimization without semidefinite programming

Author

Papp, Dávid and Yıldız, Sercan

Subjects
Mathematics - Optimization and Control, 90C25, 90C51, 65D05, 90C22
Abstract

We propose a homogeneous primal-dual interior-point method to solve sum-of-squares optimization problems by combining non-symmetric conic optimization techniques and polynomial interpolation. The approach optimizes directly over the sum-of-squares cone and its dual, circumventing the semidefinite programming (SDP) reformulation which requires a large number of auxiliary variables. As a result, it has substantially lower theoretical time and space complexity than the conventional SDP-based approach. Although our approach avoids the semidefinite programming reformulation, an optimal solution to the semidefinite program can be recovered with little additional effort. Computational results confirm that for problems involving high-degree polynomials, the proposed method is several orders of magnitude faster than semidefinite programming., Comment: Matlab implementation of the algorithm is available at https://github.com/dpapp-github/alfonso Supplementary material is available at https://github.com/dpapp-github/certificates

Published
2017

5. On 'A Homogeneous Interior-Point Algorithm for Non-Symmetric Convex Conic Optimization'

Author

Papp, Dávid and Yıldız, Sercan

Subjects
Mathematics - Optimization and Control, 90C25, 90C51, 90C30
Abstract

In a recent paper, Skajaa and Ye proposed a homogeneous primal-dual interior-point method for non-symmetric conic optimization. The authors showed that their algorithm converges to $\varepsilon$-accuracy in $O(\sqrt{\nu}\log \varepsilon^{-1})$ iterations, where $\nu$ is the complexity parameter associated with a barrier function for the primal cone, and thus achieves the best-known iteration complexity for this class of problems. However, an earlier result from the literature was used incorrectly in the proofs of two intermediate lemmas in that paper. In this note, we propose new proofs of these results, allowing the same complexity bound to be established., Comment: The Matlab implementation of the algorithm is available at https://github.com/dpapp-github/alfonso

Published
2017

7. Two-Term Disjunctions on the Second-Order Cone

Author

Kilinc-Karzan, Fatma and Yildiz, Sercan

Subjects
Mathematics - Optimization and Control
Abstract

Balas introduced disjunctive cuts in the 1970s for mixed-integer linear programs. Several recent papers have attempted to extend this work to mixed-integer conic programs. In this paper we study the structure of the convex hull of a two-term disjunction applied to the second-order cone, and develop a methodology to derive closed-form expressions for convex inequalities describing the resulting convex hull. Our approach is based on first characterizing the structure of undominated valid linear inequalities for the disjunction and then using conic duality to derive a family of convex, possibly nonlinear, valid inequalities that correspond to these linear inequalities. We identify and study the cases where these valid inequalities can equivalently be expressed in conic quadratic form and where a single inequality from this family is sufficient to describe the convex hull. In particular, our results on two-term disjunctions on the second-order cone generalize related results on split cuts by Modaresi, Kilinc, and Vielma, and by Andersen and Jensen.

Published
2014

12. Üst ekstremı̇te esansı̇yel tremoruna yönelı̇k aktı̇f ve pası̇f güç kontrollü gı̇yı̇lebı̇lı̇r cı̇haz gelı̇ştı̇rı̇lmesı̇ ve etkı̇nlı̇ğı̇nı̇n araştırılması

Author

Yıldız, Sercan Doğukan, Şehirli, Ümit S., Aküner, M. Caner, Marmara Üniversitesi, Sağlık Bilimleri Enstitüsü, Anatomi Anabilim Dalı, and Anatomi Bilim Dalı

Subjects
Giyilebilir cihaz, Parkinson Wearable device, Essential tremor, Parkinson, Esansiyel tremor
Abstract

Amaç: Esansiyel tremor ve diğer tremor tipleri için de kullanılabilmesi olası aktif ve pasif güç kontrollü giyilebilir bir cihaz geliştirilmesi ve bu cihazın etkinliğinin araştırılması amaçlanmıştır. Oluşturulan giyilebilir cihaz ile birlikte tremorun sönümlenmesi hedeflenmektedir.Gereç ve Yöntem: Aktif ve pasif güç kontrollü giyilebilir bir cihaz SolidWorks (2020 SP2.0) yazılımı ile tasarlanmıştır. Tasarlanan cihazın prototipi 3d yazıcı kullanılarak oluşturulmuştur. Tasarlanan giyilebilir cihaz bilgisayar ortamında MatLab (R2021a) yazılımı ile simüle edilmiştir. Oluşturulan prototip laboratuvar ortamında test edilmiştir. 3d yazıcı kullanılarak baskısı alınan bir el modeli üzerine tremoru taklit eden bir motor yerleştirilmiştir. Bu motorun oluşturduğu 5 Hz değerindeki tremoru sönümlemek için aktif ve pasif güç kontrollü cihaz el modeline takılmıştır ve test edilmiştir. Nöroloji kliniğine başvuran esansiyel tremor hastaları ve Parkinson hastaları üzerinde cihazın etkinliği araştırılmıştır. Hastaların kullanımına sunulan cihazdan bir akselerometre ile tremora ilişkin veriler toplanmıştır.Bulgular: Giyilebilir cihazın, tremoru bilgisayar ortamında sönümlediği görülmüştür. Laboratuvar ortamında elde edilen veriler üretilen tremoru 3d baskı ile oluşturulan el modeli üzerinde sönümlemiştir. Hastalar üzerinde etkinliği değerlendirilen giyilebilir cihazın akselerometre verilerine bakıldığında tremorun amplitudunun küçüldüğü ve frekansının değişmediği görüşmüş olup tremorun sönümlenmesinde başarı sağlanmıştır.Sonuç: Giyilebilir cihaz prototipi simülasyon, laboratuvar ortamında ve klinik çalışmalarda tremorun sönümlenmesinde başarı sağlamıştır. ET ve PH`da cihaz tremoru semptomunu ortadan kaldırmaya yönelik olarak başarı ile kullanılabilir.Anahtar kelimeler: Giyilebilir Cihaz, Esansiyel Tremor, Parkinson Objective: It is aimed to develop a wearable device that can be used for essential and other types of tremor and to investigate the effectiveness of this device. With this device, it is aimed to dampen the tremor.Material and Methods: A wearable device was designed. The prototype of the designed device was created using a 3d printer. The device was simulated in computer environment. The printed prototype has been tested in the laboratory. A motor that produces tremor is placed on a hand which is printed using a 3D printer. In order to dampen the 5 Hz tremor created, wearable device has been attached to the hand model and tested. The effectiveness of the device was investigated on essential tremor patients and Parkinson patients who applied to the neurology clinic. Data on tremor were collected with an accelerometer.Results: It has been observed that the wearable device dampens the tremor in the simulation. The data obtained in the laboratory environment damped the produced tremor on the hand model created with 3d printing. Considering the accelerometer data of the wearable device, it was observed that the amplitude of the tremor decreased, and success was achieved in the attenuation of the tremor.Conclusion: The wearable device prototype has been successful in damping tremor in simulation environment, laboratory environment and clinical studies. It can be used successfully to eliminate the symptom of device tremor in ET and PH.Keywords: Wearable device, Essential Tremor, Parkinson

Published
2023

13. Two-Term Disjunctions on the Second-Order Cone

Author

Kılınç-Karzan, Fatma, Yıldız, Sercan, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Kobsa, Alfred, editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Weikum, Gerhard, editor, Lee, Jon, editor, and Vygen, Jens, editor

Published
2014
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23. Neuroprotective effect of regular swimming exercise on calretinin-positive striatal neurons of Parkinsonian rats

Author

Özlem Kirazlı, Ümit Şehirli, Rezzan Gülhan, H Boracı, and D Yıldız Sercan

Subjects
Male, medicine.medical_specialty, Parkinson's disease, Swimming exercise, Striatum, Neuroprotection, 03 medical and health sciences, Interneurons, Internal medicine, Physical Conditioning, Animal, Medicine, Animals, Rats, Wistar, Medial forebrain bundle, Oxidopamine, Swimming, 030304 developmental biology, 0303 health sciences, Tyrosine hydroxylase, business.industry, Parkinson Disease, General Medicine, medicine.disease, Corpus Striatum, Disease Models, Animal, Endocrinology, nervous system, 030301 anatomy & morphology, Calbindin 2, Anatomy, Calretinin, business, Perfusion
Abstract

In Parkinson’s disease (PD), physical therapy is one of the mainstays of supportive treatment modalities. This study focused on the neuroprotective effect of regular exercise on striatal calretinin positive interneurons in a rat model of PD. 6-hydroxydopamine (6-OHDA) was injected unilaterally into the medial forebrain bundle of Wistar rats. 6-OHDA lesioned (Parkinsonian) and unlesioned (control) rats were divided into sedentary and exercise groups. Exercise groups had daily swimming sessions for 30 min for 6 weeks. After 6-OHDA injections, an apomorphine-induced rotation test was performed (0.05 mg/kg, subcutaneous) at the 3rd and 6th weeks. At the end of the 6th week, brains were removed following transcardiac perfusion. The brain sections were stained immunohistochemically for tyrosine hydroxylase and calretinin reactivity. The number of rotations was significantly lower in Parkinsonian exercise group compared to Parkinsonian sedentary group at the 6th week (p = 0.024) and there was significant difference between Parkisonian sedentary groups at the 3rd and 6th weeks (p

Published
2019

24. Turizm Meslek Lisesi Öğrencilerinin Demografik Değişkenlerine Göre Mesleki Bağlılık Düzeylerinin İncelenmesi

Author

Yıldız, Sercan, Göktaş, Levent Selman, Habil, Tuncay, and İstanbullu Dinçer, Fatma Füsun

Subjects
Research Subject Categories::SOCIAL SCIENCES
Abstract

Bu araştırma, İstanbul’da bir Mesleki ve Teknik Anadolu Lisesinde turizm eğitimi gören ve en az bir dönem turizm sektöründe staj yapmış 11. ve 12. Sınıf öğrencilerinin demografik özelliklerine göre turizme yönelik mesleki bağlılık düzeylerini belirlemek amacıyla yapılmıştır. Öğrencilerin mesleki bağlılık düzeylerinin belirlenmesinde, Meyer ve diğerleri (1993) tarafından ortaya atılan ve Tak ve Çiftçioğlu (2009) tarafından Türkçe’ye çevrilerek güvenilirlik ve geçerlilik çalışması yapılan, “Mesleki Bağlılık Ölçeği" kullanılmıştır. Veriler, okul idaresi tarafından 2016-2017 eğitim-öğretim yılında 11. ve 12. sınıfta öğrenim gören 290 öğrenciden anket tekniği ile toplanmıştır. Man Whitney-U testi ile gerçekleştirilen hipotez testleri sonucunda, öğrencilerin cinsiyet ve en son staj yaptıkları işletme özelliklerine göre, turizm mesleğine yönelik bağlılık düzeylerinde anlamlı farklılıklar tespit edilmiştir. Ayrıca araştırma sonuçları, öğrencilerin sınıf düzeylerine göre mesleki bağlılık düzeylerinde anlamlı bir farklılık olmadığını göstermektedir., This research was conducted so as to determine the level of professional commitment towards tourism according to some demographic characteristics of 11th and 12th grade students who have been trained tourism in a Vocational and technical Anatolian High School in Istanbul and who have completed at least one term internship in tourism sector. In determining the level of professional commitment of students, "Professional Commitment Scale" by put forward Meyer et al. and Tak and Çiftçioğlu translated it into Turkish and conducted a reliability and validity study is used. Data were collected with questionnaire technique by the school administration from 290 students in 11th and 12th grade studying in the 2016-2017 academic year. As a result of the hypothesis tests performed by the Man Whitney-U test, significant differences were found in the level of commitment towards tourism profession, according to the students' gender and the characteristics of the business to do their internship. Also the results of the research show that there is no significant difference in the level of professional commitment according to the class levels of the students.

Published
2019

26. Turizm Fakültesi Öğrencilerinin Bazı Demografik Özelliklerine Göre Serbest Zaman Motivasyonlarının İncelenmesi: Akdeniz Üniversitesi Örneği

Author

Yıldız, Sercan and Dinçer, Mithat Zeki

Subjects
Research Subject Categories::SOCIAL SCIENCES
Abstract

Bu araştırma, Akdeniz Üniversitesi Turizm Fakültesi öğrencilerinin bazı demografik özelliklerine göre, serbest zaman faaliyetleri motivasyon düzeylerine yönelik muhtemel anlamlı farklılıkların belirlenmesi amacıyla yapılmıştır. Serbest zaman motivasyon düzeyinin belirlenmesinde Beard ve Ragheb (1983, p.228) tarafından geliştirilen “Serbest Zaman Motivasyonu Ölçeği (LMS)” kullanılmıştır. Veriler, 2015-2016 EğitimÖğretim yılı içerisinde Akdeniz Üniversitesi, Turizm Fakültesi’nde öğrenim gören 230 öğrenciden toplanmış ve Anova Analizi ve Bağımsız Örneklem T-Testi yardımı ile analiz edilmiştir. Araştırma sonuçları, öğrencilerin cinsiyet, yaş ve sınıf özelliklerine göre, rekreasyonel faaliyetlere katılma motivasyonlarında anlamlı farklılıklar olduğunu göstermektedir. Ortaya çıkan bu sonuçlar gerek fakülte gerekse üniversite yönetimine, öğrencilere yönelik rekreasyonel faaliyetler düzenlerken yol gösterici nitelikte olabilir., This research was conducted to determine the possible meaningful differences in the level of leisure time motivation according to some demographic characteristics of the Akdeniz University, Faculty of Tourism students. The "Leisure Time Motivation Scale (LMS)" developed by Beard and Ragheb (1983, p.228) was used to determine the level of leisure time motivation. The data were collected from 230 students studying in the departments of Travel Management, Hospitality Management and Food and Beverage Management of the Faculty of Tourism during 2015-2016 academic year and analyzed with Anova and Independent Sample T-Test. The results of the research reveal that there is a significant difference in the motivation of students to participate in recreational activities according to gender, age and class characteristics. The results can be guiding to faculty and university managers in order to arrange recreational activities for students.

Published
2017

32. Quiet Quitting: Causes, Consequences and Suggestions

Author

Sercan Yıldız and Yıldız, Sercan

Subjects
Quite Quitting, Business, Covid-19, Labor Markerts, Organizational Behavior, Great Resignation
Abstract

The 21st century is pushing businesses like never before. After the Covid-19 pandemic, a new danger has emerged for businesses that have started to recover and return to regular working hours. This study aimed to define quiet quitting, determine the potential risks for businesses, and reveal the precautions to be taken against it. Although quiet quitting is a new concept in the literature, holistic studies on the potential risks for businesses and the precautions to be taken against quiet quitting have yet to be found. Therefore, to contribute to the literature, the concept of quiet quitting has been qualitatively examined and defined. In addition, the factors that reveal the concept of quiet quitting are stated. Subsequently, the potential risks that may be encountered due to quiet quitting businesses are mentioned. Finally, some suggestions have been presented to the business to prevent quiet quitting. The study is anticipated to contribute to the literature for future research.

Published
2023

33. Morphometric analysis of middle and posterior cranial fossae foramina in 3D reconstructions of CT images: A midline asymmetry evaluation

Author

Ural VERIMLI, Onur BUGDAYCI, Sercan Dogukan YILDIZ, Emrah OZKILIC, Nural BEKIROGLU, Omer OZDOGMUS, İstanbul Kent Üniversitesi, Fakülteler, Sağlık Bilimleri Fakültesi, Dil ve Konuşma Terapisi Bölümü, Yıldız, Sercan Doğukan, and VERİMLİ U., BUĞDAYCI O., Yildiz S. D., Ozkilic E., BEKİROĞLU G. N., ÖZDOĞMUŞ N. Ö.

Subjects
Midline, Temel Tıp Bilimleri, Medicine (miscellaneous), Assessment and Diagnosis, Sağlık Bilimleri, Fundamental Medical Sciences, Pathophysiology, Clinical Medicine (MED), REGION, TIP, GENEL & DAHİLİ, Health Sciences, Internal Medicine, Asymmetry,Computed tomography,Cranial fossa,Foramen,Midline, Klinik Tıp (MED), SKULL BASE, MEDICINE, GENERAL & INTERNAL, Computed tomography, SPINOSUM, Klinik Tıp, OVALE, Fundamentals and Skills, Asymmetry, General Medicine, CLINICAL MEDICINE, Cranial fossa, Tıp, ARTERY BYPASS, Foramen, General Health Professions, Medicine, Family Practice
Abstract

Objective: The cranial base harbours numerous foramina, and the anatomical properties of the foramina are crucial in clinical interventions. The purpose of the current study is to evaluate possible asymmetries regarding the middle and posterior cranial fossae foramina using 3D reconstructions of high-resolution computed tomography (CT) images. Patients and Methods: High-resolution cranial CT images of 253 female and 287 male adult patients were used in the study. The patients were 18 to 40 years of age without any apparent cranial pathology. The distances from the foramen rotundum, foramen ovale, foramen spinosum, internal acoustic meatus, hypoglossal canal to the midline were measured bilaterally to compare both sides. Results: The foramen spinosum and the mid-clival line measurements demonstrated statistically significant results favoring the right side (p=0.03, right mean 3.052 ± 0.253 cm, left mean 2.982 ± 0.193 cm). In males, the right foramen spinosum to mid-clival line measurements were significantly longer than the left side (p=0.027, right mean 3.150 ± 0.250 cm, left mean 3.070 ± 0.180 cm). Conclusion: As predicted, the male measurements were significantly longer than the female measurements regardless of sides in all measurements. The measurements of cranial asymmetries may help describe anomalies and may contribute to the clinical approaches.

Published
2022

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