A robust numerical technique for solving non-linear Volterra integro-differential equations with boundary layer

Firat Cakir,Musa Cakir,Hayriye Guckir Cakir 대한수학회 2022 대한수학회논문집 Vol.37 No.3

In this paper, we study a first-order non-linear singularly perturbed Volterra integro-differential equation (SPVIDE). We discretize the problem by a uniform difference scheme on a Bakhvalov-Shishkin mesh. The scheme is constructed by the method of integral identities with exponential basis functions and integral terms are handled with interpolating quadrature rules with remainder terms. An effective quasi-linearization technique is employed for the algorithm. We establish the error estimates and demonstrate that the scheme on Bakhvalov-Shishkin mesh is $O(N^{-1})$ uniformly convergent, where $N$ is the mesh parameter. The numerical results on a couple of examples are also provided to confirm the theoretical analysis.

Influence of wall flexibility on dynamic response of cantilever retaining walls

Cakir, Tufan Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.1

A seismic evaluation is made of the response to horizontal ground shaking of cantilever retaining walls using the finite element model in three dimensional space whose verification is provided analytically through the modal analysis technique in case of the assumptions of fixed base, complete bonding behavior at the wall-soil interface, and elastic behavior of soil. Thanks to the versatility of the finite element model, the retained medium is then idealized as a uniform, elastoplastic stratum of constant thickness and semi-infinite extent in the horizontal direction considering debonding behavior at the interface in order to perform comprehensive soil-structure interaction (SSI) analyses. The parameters varied include the flexibility of the wall, the properties of the soil medium, and the characteristics of the ground motion. Two different finite element models corresponding with flexible and rigid wall configurations are studied for six different soil types under the effects of two different ground motions. The response quantities examined incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that the wall flexibility and soil properties have a major effect on seismic behavior of cantilever retaining walls and should be considered in design criteria of cantilever walls. Furthermore, the results of the numerical investigations are expected to be useful for the better understanding and the optimization of seismic design of this particular type of retaining structure.

Experimental analysis on FEM definition of backfill-rectangular tank-fluid system

Cakir, Tufan,Livaoglu, Ramazan Techno-Press 2013 Geomechanics & engineering Vol.5 No.2

In the present study, the numerical and experimental investigations were performed on the backfill- exterior wall-fluid interaction systems in case of empty and full tanks. For this, firstly, the non-linear three dimensional (3D) finite element models were developed considering both backfill-wall and fluid-wall interactions, and modal analyses for these systems were carried out in order to acquire modal frequencies and mode shapes by means of ANSYS finite element structural analysis program. Secondly, a series of field tests were fulfilled to define their modal characteristics and to compare the results from proposed approximation in the selected structures. Finally, comparing the theoretical predictions from the finite element models to results from experimental measurements, a close agreement was found between theory and experiment. Thus, it can be easily stated that experimental verifications provide strong support for the finite element models and the proposed procedures themselves are the meritorious approximations to the real problem, and this makes the models appealing for use in further investigations.

Backfill and subsoil interaction effects on seismic behavior of a cantilever wall

Cakir, Tufan Techno-Press 2014 Geomechanics & engineering Vol.6 No.2

The main focus of the current study is to evaluate the dynamic behavior of a cantilever retaining wall considering backfill and soil/foundation interaction effects. For this purpose, a three-dimensional finite element model (FEM) with viscous boundary is developed to investigate the seismic response of the cantilever wall. To demonstrate the validity of the FEM, analytical examinations are carried out by using modal analysis technique. The model verification is accomplished by comparing its predictions to results from analytical method with satisfactory agreement. The method is then employed to further investigate parametrically the effects of not only backfill but also soil/foundation interactions. By means of changing the soil properties, some comparisons are made on lateral displacements and stress responses. It is concluded that the lateral displacements and stresses in the wall are remarkably affected by backfill and subsoil interactions, and the dynamic behavior of the cantilever retaining wall is highly sensitive to mechanical properties of the soil material.

Comparison of Three Dimensional Conformal Radiation Therapy, Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy for Low Radiation Exposure of Normal Tissue in Patients with Prostate Cancer

Cakir, Aydin,Akgun, Zuleyha,Fayda, Merdan,Agaoglu, Fulya Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.8

Radiotherapy has an important role in the treatment of prostate cancer. Three-dimensional conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques are all applied for this purpose. However, the risk of secondary radiation-induced bladder cancer is significantly elevated in irradiated patients compared surgery-only or watchful waiting groups. There are also reports of risk of secondary cancer with low doses to normal tissues. This study was designed to compare received volumes of low doses among 3D-CRT, IMRT and VMAT techniques for prostate patients. Ten prostate cancer patients were selected retrospectively for this planning study. Treatment plans were generated using 3D-CRT, IMRT and VMAT techniques. Conformity index (CI), homogenity index (HI), receiving 5 Gy of the volume (V5%), receiving 2 Gy of the volume (V2%), receiving 1 Gy of the volume (V1%) and monitor units (MUs) were compared. This study confirms that VMAT has slightly better CI while thev olume of low doses was higher. VMAT had lower MUs than IMRT. 3D-CRT had the lowest MU, CI and HI. If target coverage and normal tissue sparing are comparable between different treatment techniques, the risk of second malignancy should be a important factor in the selection of treatment.

Assessment of effect of material properties on seismic response of a cantilever wall

Cakir, Tufan Techno-Press 2017 Geomechanics & engineering Vol.13 No.4

Cantilever retaining wall movements generally depend on the intensity and duration of ground motion, the response of the soil underlying the wall, the response of the backfill, the structural rigidity, and soil-structure interaction (SSI). This paper investigates the effect of material properties on seismic response of backfill-cantilever retaining wall-soil/foundation interaction system considering SSI. The material properties varied include the modulus of elasticity, Poisson's ratio, and mass density of the wall material. A series of nonlinear time history analyses with variation of material properties of the cantilever retaining wall are carried out by using the suggested finite element model (FEM). The backfill and foundation soil are modelled as an elastoplastic medium obeying the Drucker-Prager yield criterion, and the backfill-wall interface behavior is taken into consideration by using interface elements between the wall and soil to allow for de-bonding. The viscous boundary model is used in three dimensions to consider radiational effect of the seismic waves through the soil medium. In the seismic analyses, North-South component of the ground motion recorded during August 17, 1999 Kocaeli Earthquake in Yarimca station is used. Dynamic equations of motions are solved by using Newmark's direct step-by-step integration method. The response quantities incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that while the modulus of elasticity has a considerable effect on seismic behavior of cantilever retaining wall, the Poisson's ratio and mass density of the wall material have negligible effects on seismic response.

Are Platelet Indices such as Platelet Volume, Platelet Distribution Width, and Plateletcrit Associated with Peyronie Disease?

Cakir Suleyman Sami,Ozbir Sait,Atalay Hasan Anıl,Culha Mehmet Gokhan,Can Osman,Canat Halil Lütfi 대한남성과학회 2020 The World Journal of Men's Health Vol.38 No.3

Purpose: Peyronie disease (PD) occurs as a result of recurrent microvascular injuries or trauma of the tunica albuginea, although its precise etiology is unknown. Mean platelet volume (MPV), platelet distribution width (PDW), and plateletcrit (PCT), which are parameters indicative of platelet activity, are considered to be functional markers of platelets involved in the pathophysiology of related inflammatory and vascular diseases. In this study, we aimed to examine the relationship between PD and platelet indices. Materials and Methods: We evaluated participants who presented to the andrology department of our institution between December 2015 and May 2018. Ninety-two men with PD and 80 healthy volunteers were included in this study. Participants who had received medical treatment affecting platelets or had any hematologic or systemic diseases were excluded from the study. Results: The mean age of men with PD was 53.8±10.2 years, and the mean age of the control group was 52.2±8.0 years (p=0.465). There were no significant differences in the mean IIEF-5 scores, platelet count, MPV, PDW, or PCT between the patients with and without PD (p<0.05). Conclusions: No correlations were found between PD and platelet indices. Large-scale prospective cross-sectional studies are needed to elucidate the etiopathogenesis of PD.

Neurocognitive Functions in Infants with Malnutrition; Relation with Long-chain Polyunsaturated Fatty Acids, Micronutrients Levels and Magnetic Resonance Spectroscopy

Cakir, Murat,Senyuva, Sukran,Kul, Sibel,Sag, Elif,Cansu, Ali,Yucesan, Fulya Balaban,Yaman, Serap Ozer,Orem, Asim The Korean Society of Pediatric Gastroenterology 2019 Pediatric gastroenterology, hepatology & nutrition Vol.22 No.2

Purpose: Malnutrition may influence neurocognitive development in children by directly affecting the brain structural development, or indirectly by affecting the children's cognition experience. Malnutrition alters the cell numbers, cell migration, synaptogenesis, and neurotransmission due to inadequate availability of necessary micronutrients to support cell growth. We aimed to analyze neurocognitive development in infants with malnutrition and its association with long chain polyunsaturated fatty acids (LC-PUFA), micronutrients levels and magnetic resonance spectroscopy (MRS) findings. Methods: The study included two groups; group 1, infants with malnutrition (n=24), group 2; healthy infants (n=21). Peripheral blood was obtained from the participants for studying micronutrients and LC-PUFA levels. The neurocognitive development was analyzed by the use of an Ankara Developmental Screening Inventory test. MRS were performed on all infants. Results: All parameters of neurocognitive development and serum calcium ($9.6{\pm}0.9mg/dL$ vs. $10.4{\pm}0.3mg/dL$, p<0.05) and magnesium ($2.02{\pm}0.27mg/dL$ vs. $2.2{\pm}0.14mg/dL$, p<0.05) levels were noted as being low in infants with marked malnutrition. No difference was found in LC-PUFA levels between healthy and malnourished infants. Thalamic choline/creatine levels were significantly high in infants with malnutrition ($1.33{\pm}0.22$ vs. $1.18{\pm}0.22$, p<0.05). Total neurocognitive development in infants was positively correlated with serum calcium levels (p<0.05, r=0.381). Conclusion: Calcium supplementation may improve neurocognitive development in malnourished infants.

Liver Involvement in Children with Alpha-1 Antitrypsin Deficiency: A Multicenter Study

Cakir, Murat,Sag, Elif,Islek, Ali,Baran, Masallah,Tumgor, Gokhan,Aydogdu, Sema The Korean Society of Pediatric Gastroenterology 2020 Pediatric gastroenterology, hepatology & nutrition Vol.23 No.2

Purpose: Alpha-1 antitrypsin deficiency (A1ATD) in one of the most common genetic causes of liver disease in children. We aimed to analyze the clinical characteristics and outcomes of patients with A1ATD. Methods: This study included patients with A1ATD from five pediatric hepatology units. Demographics, clinical findings, genetics, and outcome of the patients were recorded (n=25). Results: Eight patients (32.0%) had homozygous PiZZ genotype while 17 (68.0%) had heterozygous genotype. Patients with PiZZ genotype had lower alpha-1 antitrypsin levels than patients with PiMZ genotype (37.6±7.7 mg/dL vs. 66.5±22.7 mg/dL, p=0.0001). Patients with PiZZ genotype were diagnosed earlier than patients with PiMZ genotype, but this was not significant (13±6.8 months vs. 23.7±30.1 months, p=0.192). Follow-up revealed the death of one patient (12.5%) with a homozygous mutation, and revealed that one patient had child A cirrhosis, five patients (62.5%) had chronic hepatitis, and one patient (12.5%) was asymptomatic. Nine of the 17 patients with a heterozygous mutation had chronic hepatitis (52.9%), two (11.7%) had child A cirrhosis, and six (35.2%) were asymptomatic. Overall, 18 (72%) of the 25 children had liver pathology in the long-term. Conclusion: Although prevalence is rare, patients with liver disorders should be checked for alpha-1 antitrypsin levels. Moreover, long-term follow-up is essential because most patients have a liver pathology.

Disseminated Cytomegalovirus Infection and Protein Losing Enteropathy as Presenting Feature of Pediatric Patient with Crohn's Disease

Cakir, Murat,Ersoz, Safak,Akbulut, Ulas Emre The Korean Society of Pediatric Gastroenterology 2015 Pediatric gastroenterology, hepatology & nutrition Vol.18 No.1

We report a pediatric patient admitted with abdominal pain, diffuse lower extremity edema and watery diarrhea for two months. Laboratory findings including complete blood count, serum albumin, lipid and immunoglobulin levels were compatible with protein losing enteropathy. Colonoscopic examination revealed diffuse ulcers with smooth raised edge (like "punched out holes") in the colon and terminal ileum. Histopathological examination showed active colitis, ulcerations and inclusion bodies. Immunostaining for cytomegalovirus was positive. Despite supportive management, antiviral therapy, the clinical condition of the patient worsened and developed disseminated cytomegalovirus infection and the patient died. Protein losing enteropathy and disseminated cytomegalovirus infection a presenting of feature in steroid-naive patient with inflammatory bowel disease is very rare. Hypogammaglobulinemia associated with protein losing enteropathy in Crohn's disease may predispose the cytomegalovirus infection in previously healthy children.