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Öğe Geometry and Material Comparisons of Mandibular Mini-Plate Fixators According to Fracture Types, a Finite Element Study(Amer Scientific Publishers, 2014) Özkan, Arif; Atik, FatihThe purpose of the present study is to compare the plate geometries and materials for calculating stress distributions and displacements. A model of the mandible was modeled aided with computed tomography (CT) images. The CT images were converted to the finite element model aided by reverse engineering methodology. 3 materials for mini plate and fixators (Titanium Alloy, Chrome-Cobalt and Stainless Steel) were designed with different geometry variations ("Y", "I" and "Square") and two different fracture types (linear and oblique). The finite element analyses (FEA) (In Slico) were performed with respect to displacement and stress distributions for both mandibula and fixators. According to all FEA results, "Square" type fixators for linear fracture type had a minimum stress distribution. In addition, the "I" type double fixators (for oblique fractures) with titanium alloy have more favorable stress distribution and also chrome-cobalt material for have best displacement results than the others. FEA is useful for comparing geometry and material variations of rigid mandibular fixations. The finite-element method showed that when selecting mini plate we consider geometry and material variations.Öğe Effects of Ageing and Sex on Complexity in the Human Sleep EEG: A Comparison of Three Symbolic Dynamic Analysis Methods(Wiley-Hindawi, 2019) Tosun, Pınar Deniz; Dijk, Derk-Jan; Sommerer, Raphaelle Winsky; Abasolo, DanielSymbolic dynamic analysis (SDA) methods have been applied to biomedical signals and have been proven efficient in characterising differences in the electroencephalogram (EEG) in various conditions (e.g., epilepsy, Alzheimer's, and Parkinson's diseases). In this study, we investigated the use of SDA on EEGs recorded during sleep. Lempel-Ziv complexity (LZC), permutation entropy (PE), and permutation Lempel-Ziv complexity (PLZC), as well as power spectral analysis based on the fast Fourier transform (FFT), were applied to 8-h sleep EEG recordings in healthy men (n=31) and women (n=29), aged 20-74 years. The results of the SDA methods and FFT analysis were compared and the effects of age and sex were investigated. Surrogate data were used to determine whether the findings with SDA methods truly reflected changes in nonlinear dynamics of the EEG and not merely changes in the power spectrum. The surrogate data analysis showed that LZC merely reflected spectral changes in EEG activity, whereas PE and PLZC reflected genuine changes in the nonlinear dynamics of the EEG. All three SDA techniques distinguished the vigilance states (i.e., wakefulness, REM sleep, NREM sleep, and its sub-stages: stage 1, stage 2, and slow wave sleep). Complexity of the sleep EEG increased with ageing. Sex on the other hand did not affect the complexity values assessed with any of these three SDA methods, even though FFT detected sex differences. This study shows that SDA provides additional insights into the dynamics of sleep EEG and how it is affected by ageing.Öğe Differential efficiency of transcutaneous electrical nerve stimulation in dominant versus nondominant hands in fibromyalgia: placebo-controlled functional near-infrared spectroscopy study(Spie-Soc Photo-Optical Instrumentation Engineers, 2018) Eken, Aykut; Kara, Murat; Baskak, Bora; Baltacı, Ayşegül; Gökçay, DidemUsing functional near-infrared spectroscopy (fNIRS), modulation of hemodynamic responses by transcutaneous electrical nerve stimulation (TENS) during delivery of nociceptive stimulation was investigated in fibromyalgia (FM) patients and healthy controls for both hands. Two experiments were conducted: (1) median nerve stimulation with TENS and (2) painful stimulation using electronic von Frey filaments with TENS/placebo TENS. Mean Delta HbO(2) brain activity was compared across groups and conditions using factorial ANOVA. Dominant (right) hand stimulation indicated significant interactions between group and condition in both hemispheres. Post hoc results revealed that FM patients showed an increased activation in "pain + TENS" condition compared to the "pain + placebo TENS" condition while the brain activity patterns for these conditions in controls were reversed. Left-hand stimulation resulted in similar TENS effects (reduced activation for "pain + TENS" than " pain + placebo TENS") in both groups. TENS effects in FM patients might be manipulated by the stimulation side. While the nondominant hand was responsive to TENS treatment, the dominant hand was not. These results indicate that stimulation side might be an effective factor in FM treatment by using TENS. Future studies are needed to clarify the underlying mechanism for these findings. (c) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE).Öğe The relationship between medial meniscal subluxation and stress distribution pattern of the knee joint: Finite element analysis(Elsevier, 2016) Gökkuş, Kemal; Atmaca, Halil; Uğur, Levent; Özkan, Arif; Aydın, Ahmet TuranBackground: Degenerative changes of the knee joint and clinical follow-up after meniscal subluxation are well documented. In the current study three-dimensional (3D) finite element analysis (FEA) of human lower limb was used to investigate the effect medial meniscal subluxation on the loadings of the knee structures. Methods: Apart from the reference model, a total of ten 3D models were created, according to amount of medial meniscal subluxation. ANSYS (R) 14 was used to analyze the stress/load distribution, that is to say the maximum equivalent stress (MES) (von Mises stress) on bones, cartilages, ligaments and menisci. MES was expressed as Newton/mm(2) = Megapascal (MPa). Results: In a static and standing upright position the MES on all knee structures were evaluated in the reference model. Although MES increased in all structures with the increase of medial meniscal subluxation degree, tibia cartilage was found to be the most affected structure with an increase of 22.73-fold in the 10 mm subluxation model when compared with references values. Conclusion: This study showed that medial meniscus subluxation is associated with increased loadings on all knee structures especially the tibia cartilage. Also the degree of the medial meniscal subluxation correlates with distribution and the amount of loadings on tibia cartilage which may be a prominent feature of knee osteoarthritis. (C) 2015 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.Öğe The effect of proximal tibial corrective osteotomy on menisci, tibia and tarsal bones: a finite element model study of tibia vara(Wiley-Blackwell, 2014) Atmaca, Halil; Özkan, Arif; Mutlu, İbrahim; Çelik, Talip; Uğur, Levent; Kişioğlu, YasinBackgroundProximal tibial open wedge osteotomy (PTO) is a corrective operation used in the surgery of lower extremities and is applied to patients with varus deformities for sufficient correction. The aim of the study was to evaluate whether the PTO can achieve decreased stress-bearing on the tibia and tarsal bones in addition to correcting the mechanical axis of the lower limb in patients with tibia vara. MethodsThree-dimensional (3D) solid modelling of the lower extremity was carried out using computed tomography (CT) and magnetic resonance (MR)-containing images of all of the bony elements and non-bony structures. PTO was applied to the obtained deformed model in the computer environment and the correction was carried out. ResultsStress distributions in menisci, tibia and tarsal bones were calculated. With respect to loading on the tarsal bones, the maximum equivalent stresses on all bones decreased except for the navicula in the PTO-simulated model in the current study. ConclusionThese results clearly indicate that PTO can achieve decreased stresses on the tarsal bones in patients with tibia vara. Copyright (c) 2013 John Wiley & Sons, Ltd.Öğe The Effect of Gaussian Noise on Maximum Likelihood Fitting of Gompertz and Weibull Mortality Models with Yeast Lifespan Data(Taylor & Francis Inc, 2019) Güven, Emine; Akçay, Sevinç; Qin, HongBackground/study context: Empirical lifespan data sets are often studied with the best-fitted mathematical model for aging. Here, we studied how experimental noises can influence the determination of the best-fitted aging model. We investigated the influence of Gaussian white noise in lifespan data sets on the fitting outcomes of two-parameter Gompertz and Weibull mortality models, commonly adopted in aging research. Methods: To un-equivocally demonstrate the effect of Gaussian white noises, we simulated lifespans based on Gompertz and Weibull models with added white noises. To gauge the influence of white noise on model fitting, we defined a single index, , for the difference between the maximal log-likelihoods of the Weibull and Gompertz model fittings. We then applied the approach using experimental replicative lifespan data sets for the laboratory BY4741 and BY4742 wildtype reference strains. Results: We systematically evaluated how Gaussian white noise can influence the maximal likelihood-based comparison of the Gompertz and Weibull models. Our comparative study showed that the Weibull model is generally more tolerant to Gaussian white noise than the Gompertz model. The effect of noise on model fitting is also sensitive to model parameters. Conclusion: Our study shows that Gaussian white noise can influence the fitting of an aging model for yeast replicative lifespans. Given that yeast replicative lifespans are hard to measure and are often pooled from different experiments, our study highlights that interpreting model fitting results should take experimental procedure variation into account, and the best fitting model may not necessarily offer more biological insights.Öğe The effect of cement on hip stem fixation: a biomechanical study(Springer, 2017) Çelik, Talip; Mutlu, İbrahim; Özkan, Arif; Kişioğlu, YasinThis study presents the numerical analysis of stem fixation in hip surgery using with/without cement methods since the use of cement is still controversial based on the clinical studies in the literature. Many different factors such as stress shielding, aseptic loosening, material properties of the stem, surgeon experiences etc. play an important role in the failure of the stem fixations. The stem fixation methods, cemented and uncemented, were evaluated in terms of mechanical failure aspects using computerized finite element method. For the modeling processes, three dimensional (3D) femur model was generated from computerized tomography (CT) images taken from a patient using the MIMICS Software. The design of the stem was also generated as 3D CAD model using the design parameters taken from the manufacturer catalogue. These 3D CAD models were generated and combined with/without cement considering the surgical procedure using SolidWorks program and then imported into ANSYS Workbench Software. Two different material properties, CoCrMo and Ti6Al4V, for the stem model and Poly Methyl Methacrylate (PMMA) for the cement were assigned. The material properties of the femur were described according to a density calculated from the CT images. Body weight and muscle forces were applied on the femur and the distal femur was fixed for the boundary conditions. The calculations of the stress distributions of the models including cement and relative movements of the contacts examined to evaluate the effects of the cement and different stem material usage on the failure of stem fixation. According to the results, the use of cement for the stem fixation reduces the stress shielding but increases the aseptic loosening depending on the cement crack formations. Additionally, using the stiffer material for the stem reduces the cement stress but increases the stress shielding. Based on the results obtained in the study, even when taking the disadvantages into account, the cement usage is more suitable for the hip fixations.Öğe Stress distribution comparisons of foot bones in patient with tibia vara: a finite element study(Wroclaw Univ Technology, 2013) Özkan, Arif; Atmaca, Halil; Mutlu, İbrahim; Çelik, Talip; Uğur, Levent; Kişioğlu, YasinBlount's disease, or tibia vara, is the most common cause of pathologic genu varum in children and adolescents. Changes in the loading of knee structures such as tibial articular cartilage, menisci and subcondral bone are well documented in case of genu varum. But the mechanical effects of this condition on foot bones are still questionable. In this study, the authors hypothesized that stress distributions on foot bones might increase in patients with tibia vara when compared with patients who had normal lower extremity mechanical axis. Three-dimensional (3D) finite element analyses of human lower limb were used to investigate and compare the loading on foot bones in normal population and patient with tibia vara. The segmentation software, MIMICS was used to generate the 3D images of the bony structures of normal and varus malalignment lower extremity. Except the spaces between the adjacent surface of the phalanges fused, metatarsals, cuneiforms, cuboid, navicular, talus and calcaneus bones were independently developed to form foot and ankle complex. Also femur, tibia and fibula were modeled utilizing mechanical axis. ANSYS version 14 was used for mechanical tests and maximum equivalent stresses (MES) were examined. As a result of the loading conditions, in varus model MES on talus, calcaneus and cuboid were found higher than in normal model. And stress distributions changed through laterally on middle and fore foot in varus deformity model.Öğe Stress Distribution Comparisions of Fixed and Broken Fibula, a Finite Element Study(Amer Scientific Publishers, 2014) Özkan, Arif; Kişioğlu, YasinThe purpose of this study was to compare load carrying capacity and stress distributions of broken fibula on lower extremity under the average body weight and moment using with three-dimensional finite element analysis (FEA). The finite element (FE) models were generated from patient's computed tomography (CT) data images. The loading and the relevant boundary conditions selected according to average human body conditions for obtaining the stress distribution on tibia surface. According the all FE analysis fibula is an effective role for load carrying capacity on distal side of tibia. These FEA results showed that the loading characteristics of the fibula should be taken into account in planning medical and surgical operations.Öğe On-Line Surface Roughness Prediction by Using a Probabilistic Approach for End-Milling(Ieee-Inst Electrical Electronics Engineers Inc, 2019) Kayabaşı, Oğuz; Ertürk, ŞenolAn effective and efficient methodology is proposed to predict surface roughness by online monitoring of surface quality using accelerometer signals. A probabilistic approach, Monte Carlo Simulation, was researched and developed to create an automated tool for on-line prediction of surface quality. Data from 3-axis vibration (Vx, Vy, Vz) signals were used to predict on-line surface roughness. According to an experimental design with four cutting parameters (Cutting speed (Vc), Feed per teeth (Sz), Dept of cut (Dc), Width of cut (Wc)), three-axis vibration signals were used to combine data into a probabilistic model for development of an on-line surface roughness prediction system. Once the probability model was established by using a data set consisting of 71 experiments, the model was tested for 10 different cutting conditions. The probability model shows that the results have convergence values that are close to each other, by as high as 96.37%.Öğe Biomechanical analysis of titanium fixation plates and screws in mandibular angle fractures(Wolters Kluwer Medknow Publications, 2016) Atik, Fatih; Ataç, Mustafa Sancar; Özkan, Arif; Kılınç, Yeliz; Arslan, MustafaObjective: The aim of this study was to evaluate the mechanical behavior of different rigid fixation methods in mandibular angle fractures. Materials and Methods: Three different three-dimensional finite element models of the mandible were developed to simulate the biomechanical responses of titanium plates and screws. The fracture lines were fixed with double 4-hole straight, 4-hole square, and 5-hole Y plates with monocortical screws. 150 N incisal occlusal loads were simulated on the models. The commercial ANSYS software was utilized to calculate the Von Mises stresses on fixative appliances. Results: The highest Von Mises stress values were observed in the Y plate, whereas the lowest stress values have been found in the square plate. Conclusions: The use of square plate led to better stability and lower mechanical stresses than other techniques.Öğe Biomechanical analysis of titanium fixation plates and screws in sagittal split ramus osteotomies(Wolters Kluwer Medknow Publications, 2016) Atik, Fatih; Ataç, Mustafa Sancar; Özkan, Arif; Kılınç, Yeliz; Arslan, MustafaObjective: The aim of the study was to evaluate the mechanical behavior of three different fixation methods used in the bilateral sagittal split ramus osteotomy. Materials and Methods: Three different three-dimensional finite element models were created, each corresponding to three different fixation methods. The mandibles were fixed with double straight 4-hole, square 4-hole, and 5-hole Y plates. 150 N incisal occlusal loads were simulated on the distal segments. ANSYS software ((v 10; ANSYS Inc., Canonsburg, PA) was used to calculate the Von Mises stresses on fixative appliances. Results: The highest Von Mises stress values were found in Y plate. The lowest values were isolated in double straight plate group. Conclusions: It was concluded that the use of double 4-hole straight plates provided the sufficient stability on the osteotomy site when compared with the other rigid fixation methods used in this study.Öğe Binary Classification Using Neural and Clinical Features: An Application in Fibromyalgia With Likelihood-Based Decision Level Fusion(Ieee-Inst Electrical Electronics Engineers Inc, 2019) Gökçay, Didem; Eken, Aykut; Baltacı, SerdarAmong several features used for clinical binary classification, behavioral performance, questionnaire scores, test results, and physical exam reports can be counted. Attempts to include neuroimaging findings to support clinical diagnosis are scarce due to difficulties in collecting such data, as well as problems in integration of neuroimaging findings with other features. The binary classification method proposed here aims to merge small samples from multiple sites so that a large cohort, which better describes the features of the disease can be built. We implemented a simple and robust framework for detection of fibromyalgia, using likelihood during decision level fusion. This framework supports sharing of classifier applications across clinical sites and arrives at a decision by fusing results from multiple classifiers. If there are missing opinions from some classifiers due to inability to collect their input features, such degradation in information is tolerated. We implemented this method using functional near infrared spectroscopy (fNIRS) data collected from fibromyalgia patients across three different tasks. Functional connectivity maps are derived from these tasks as features. In addition, self-reported clinical features are also used. Five classifiers are trained using k nearest neighborhood (kNN), linear discriminant analysis (LDA), and support vector machine (SVM). Fusion of classification opinions from multiple classifiers based on likelihood ratios outperformed individual classifier performances. When 2, 3, 4, and 5 different classifiers are fused, sensitivity, and specificity figures of 100% could be obtained based on the choice of the classifier set.Öğe Association of Fine Motor Loss and Allodynia in Fibromyalgia: An fNIRS Study(Routledge Journals, Taylor & Francis Ltd, 2018) Eken, Aykut; Gökçay, Didem; Yılmaz, Cemre; Baskak, Bora; Baltacı, Ayşegül; Kara, MuratRecent studies showed that fine motor control dysfunction was observed in fibromyalgia (FM) syndrome as well as allodynia. However, brain signatures of this association still remain unclear. In this study, finger tapping task (FTT) and median nerve stimulation (MNS) were applied to both hands of 15 FM patients and healthy controls (HC) to understand this relationship. Hemodynamic activity was measured simultaneously using functional near-infrared spectroscopy (fNIRS). Experiments were analyzed separately by using 2x2 repeated measures ANOVA. Results for the FTT experiment revealed that HC showed higher activity than FM patients in bilateral superior parietal gyrus (SPG), left supramarginal gyrus (SMG) and right somatosensory cortex (SI). Furthermore, right-hand FTT resulted in higher activity than left-hand FTT in left SPG, left SI and right motor cortex (MI). In the MNS experiment, FM patients showed higher activity than HC in bilateral SPG, right SMG, right SI and right middle frontal gyrus (MFG). Negative correlation was observed in left SPG between FTT and MNS activities. Besides, MNS activity in left SPG was negatively correlated with left-hand pain threshold.This study revealed that left SPG might be an important indicator to associate fine motor loss and allodynia in FM.Öğe Eklemeli İmalat Yöntemleri İle Üretim ve Onarım Uygulamaları(2017) Özkan, Arif; Çelik, KadirEklemeli imalat günümüzde geleneksel üretim yöntemlerinin yetersiz veya verimsiz kaldığı çeşitli üretim işlemleri için kullanılmaktadır. Bu çalışmada, eklemeli imalatın ortaya çıkışı, gelişimi, uygulama biçimleri, bunların avantaj ve dezavantajları incelenmiştir. Farklı gereksinimler için geliştirilmiş çeşitli yöntemler, birbirleri ile kıyaslanmıştır. Hangi uygulamada hangi yöntemin tercih edilmesi gerektiği yönünde araştırmalar yapılmıştır. Çalışmada, farklı geometri, yoğunluk, malzeme ve fiziksel özellikler içeren ürünler için farklı yöntemlerin tercihinin olacağı tespit edilmiştir. Süre, malzeme miktarı, yüzey kalitesi gibi farklı etkenlerin, tercih sürecinde rol oynadığı ortaya konmuşturÖğe Tekrarlanan Yükler Altında Kompozit Malzemelerin Yapılarının İncelenmesini layan Deney Aygıtı Tasarımı(2017) Özkan, Arif; Yastımoğlu, FıratKompozit malzemeler malzeme biliminin gelişmekte olan dallarından biridir. Geleneksel üretim metotlarına uygunluğu ve özel üretim metotlarına izin vermesi nedeniyle otomotiv, denizcilik, havacılık, tekstil ve savunma sanayinde oldukça tercih edilir hale gelmiştir. Dolgu yani takviye malzeme, kompozit malzamelerde mekanik mukavemetin sağlanmasında önemli rol oynar. Kompozit malzemelerde takviye elemanı lifler, partiküller, tabaka formunda olabilir. Matris malzeme ise kompozit yapıyı birbütün halinde tutar. Aynı zamanda matris formu yapının fiziki, kimyasal, ısıl özelliklerini ve mukavemetini belirler. Matris malzemesi olarak Seramikler, Metaller ve bunların alaşımları kullanılabildiği gibi yaygın olarak reçineler tercih edilmektedir. Reçinenin tercih edilmesinin temel nedenlerinden biri imalat kolaylığı ve üretim maliyetidir. Bu çalışmada sürekli titreşim ve sürünme olayına maruz kalan kompozit malzemelerin yapılarının ve oluşturdukları ara bağ yüzeyinin analizi ve yapının ömrünün analitik olarak hesaplanabilmesini amaçlayan deney düzeneğinin tasarımı hedeflenmiştir. Deney düzeneği tasarımımda SOLIDWORKS programı kullanılmıştır. Deney numunelerinin tasarımı ve eldesi sürecinde, kompozit dolgu malzemesinin geometrisi ve yerleşim yönleri araştırılmış ve hangi şartlar altında çalışması gerektiğinin uygun olduğu araştırılmıştırÖğe Design methodology for dental implant using approximate solution techniques(Elsevier Masson SAS, 2020) Kayabaşı, OğuzWith the developing technology, dental implants have been widely used in recent years. These implants are surgically implanted into a jaw bone to support missing teeth. Implants are usually made of titanium and are biocompatible. The design and analysis of the dental implant is based on expert knowledge, experience and ability to work seamlessly on the patient. Due to the difficulties in performing dental implant tests in vivo, the geometric shape design of the dental implant must be performed before it is applied to a patient and mathematical models have been developed to perform structural analysis. In this study, a design strategy for dental implant design was proposed. In this proposed strategy, finite element analysis, numerical optimization method and probabilistic design approach Monte Carlo simulation are integrated to work together automatically. © 2020 Elsevier Masson SASÖğe Comparison of the Lag Screw Placements for the Treatment of Stable and Unstable Intertrochanteric Femoral Fractures regarding Trabecular Bone Failure(Hindawi Limited, 2016) Çelik, Talip; Mutlu, İbrahim; Özkan, Arif; Kişioğlu, YasinBackground. In this study, the cut-out risk of Dynamic Hip Screw (DHS) was investigated in nine different positions of the lag screw for two fracture types by using Finite Element Analysis (FEA). Methods. Two types of fractures (31-A1.1 and A2.1 in AO classification) were generated in the femur model obtained from Computerized Tomography images. The DHS model was placed into the fractured femur model in nine different positions. Tip-Apex Distances were measured using SolidWorks. In FEA, the force applied to the femoral head was determined according to the maximum value being observed during walking. Results. The highest volume percentage exceeding the yield strength of trabecular bone was obtained in posterior-inferior region in both fracture types. The best placement region for the lag screw was found in the middle of both fracture types. There are compatible results between Tip-Apex Distances and the cut-out risk except for posterior-superior and superior region of 31-A2.1 fracture type. Conclusion. The position of the lag screw affects the risk of cut-out significantly. Also, Tip-Apex Distance is a good predictor of the cut-out risk. All in all, we can supposedly say that the density distribution of the trabecular bone is a more efficient factor compared to the positions of lag screw in the cut-out risk. © 2016 Talip Celik et al.
