Homojen Olmayan Elastik Konik Bir Kabuğun Üniform Olmayan Yanal Dış Basınç Yükü Etkisi Altında Stabilitesi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Bu çalışmada homojen olmayan elastik kesik konik bir kabuğun uniform olmayan yanal basınç yükü etkisi altında stabilitesi incelenmiştir. Çalışmada, basit mesnetli homojen olmayan elastik malzemelerden oluşan konik kabukların temel bağıntıları çıkarılmış, değiştirilmiş Donnell tipi stabilite ve deformasyon uygunluk denklemleri elde edilmiş ve bu denklemlere Galerkin yöntemi uygulanarak uniform olmayan yanal basınç yükü için analitik ifade elde edilmiştir. Elde edilen ifade çevresel dalga sayısına göre minimize edilerek uniform olmayan kritik yanal basınç yükünün minimum değeri bulunmuştur. Son olarak da hesaplar yapılarak, koni parametrelerinin ve homojen olmamanın kuvvet fonksiyonu şeklinde değişiminin kritik yanal basınç yükü değerine etkileri incelenmiştir. Elde edilen ifadeler üzerine yapılan sayısal sonuçlar kaynaklardaki sonuçlarla karşılaştırılarak doğruluğu saptanmıştır.In this study, stability of a non-homogeneous elastic truncated conical shell under non-uniform lateral pressure is studied. Firstly, fundamental relations of conical shells made of nonhomogeneous elastic materials are expressed and modified Donnell type stability and compatibility equations are obtained. Then, applying Galerkin method to these equations, an analytical expression for non-uniform lateral pressure is get. Minimizing the obtained expression according to the circumferential wave number, minimum value of the non-uniform critical lateral pressure is found. Finally, making computations, the effects of the variations of conical shell parameters and non-homogeneity as power functions to the critical lateral pressure values are examined. Obtained results are compared with those in the literature and the validity of the study is established

Worsening of heart failure due to right ventricular apical pacing by ICD implanted after myocardial infraction and treatment with resynchronization

WOS: 000319806100023PubMed ID: 23443858

Differentiation of BMSCs into Nerve Precursor Cells on Fiber-Foam Constructs for Peripheral Nerve Tissue Engineering

Bone marrow stem cells (BMSCs) are frequently used in nerve tissue engineering studies due to ease of their isolation and high potential for differentiation into nerve cells. A bilayer fiber-foam construct containing nanofibrous elements to house and guide BMSCs was designed as a model to study the regeneration of damaged peripheral nerve tissue and eventually serve as a nerve guide. The construct consisted of a) a macroporous bottom layer to serve as the backing and support, and for nutrient transport, and b) an electrospun, fibrous upper layer for cell attachment and guidance. Porosity and pore sizes of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) bottom layer were 85% and 5-200 μm, respectively, suitable for cell attachment and growth. Alignment of the cells is essential for cell-to-cell contact and the degree of alignment of electrospun PHBV/Collagen fibers was 11° when a frame type collector was used, while it was much higher (53°) for random fibers produced on an ordinary aluminum sheet collector. When the fibers were electrospun directly onto a PHBV foam attached on the frame type collector to create the bilayer, the degree of alignment of fibers decreased, alignment angle increased from 11° to 44°. This value did not change when the fibers were electrospun directly on the foams on the aluminum collector (53° vs 55°). A new media was designed to achieve comparable differentiation with the commercial media. It was found that the commercial Mesenchymal Stem Cell Neurogenic Differentiation Medium (PromoCell, Germany) was the better in terms of the expressions of neuronal markers nestin and β-III tubulin and the medium made in the lab with known constituents led to neuronal marker expressions very close to that with the commercial medium. Attachment and proliferation of the rBMSCs were higher on the random fiber mats, while alignment of cells was higher on the aligned fibers. In conclusion, the bilayer construct with aligned PHBV-collagen fibers on a PHBV foam was found to be more appropriate for peripheral nerve repair when used as a nerve guid

A novel GeIMA-pHEMA hydrogel nerve guide for the treatment of peripheral nerve damages

Damage to the nervous system due to age, diseases or trauma may inhibit signal transfer along the nervous system. Nerve guides are used to treat these injuries by bridging the proximal and the distal end together. The design of the guide is very important for the reconnection of the severed axons. Methacrylated gelatin-poly(2-hydroxyethylmethacrylate) (GeIMA-pHEMA) hydrogel was produced as the outer part of the nerve guide. pHEMA was added in various amounts into GeIMA and increased the mechanical strength which is needed for the suturability of the guide. Porosity (15-70%), pore size (10-35 mu m), water content (42-92%), and mechanical strength (65-710 kPa) of GeIMA-pHEMA hydrogels were found to be suitable for nerve tissue engineering applications. Schwann cells attached and proliferated on GeIMA, GeIMA-pHEMA (5:5), and pHEMA hydrogels. Providing guidance is very important in the development of a nerve guide due to the anisotropic nature of the nerve tissue. Therefore, gelatin-poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) aligned fiber mats were used inside of the nerve guide. High degree of alignment with low deviation (r) of this mats provided PC12 cell alignment throughout the fibers. Combination of GeIMA-pHEMA (5:5) hydrogel and gelatin-PHBV aligned mat would provide an ideal nerve guide for the treatment of peripheral nerve damages. (C) 2018 Published by Elsevier B.V

Frailty significantly impairs the short term prognosis in elderly patients with heart failure

Background Frailty is a condition of elderly characterized by increased vulnerability to stressful events with high risk of adverse outcomes. The purpose of this study was to evaluate the association between frailty and adverse outcomes including death and hospitalization due to heart failure in elderly patients. Methods We included patients aged ? 65 years with the diagnosis of heart failure. The clinical and laboratory data, echocardiography and ECGs were recorded. Additionally, the frailty scores of the patients were evaluated according to Canadian Study of Health and Aging. All the patients were divided as frail or non-frail. The groups were compared for their characteristics and the occurrence of clinical outcomes. Results We included 86 eligible patients. The median follow-up time was four months. The mean age was 75 ± 6.5 years. Of these 86 patients, 17 (19.7%) patients encountered an event (death and/or hospitalization). Nine patients (10.4%) died during follow-up. Thirty patients (34.9%) were considered frail. Among the demographic, clinical and laboratory data, only total protein and albumin levels were found to be lower in frail patients (total protein level: 6.8 ± 0.6 g/dL in non-frails, 6.5 ± 0.9 g/dL in frails, P = 0.05; albumin level: 3.8 ± 0.4 g/dL in non-frails, 3.4 ± 0.6 g/dL in frails, P = 0.001). In multivariate analysis, frailty was found to be strongly associated with clinical outcomes in short term. Conclusions Being frail in an elderly heart failure patient is associated with death and/or hospitalization due to heart failure in short term. Therefore, frailty score should be evaluated for all elderly heart failure patients as a prognostic marker. © 2018 JGC All rights reserved