Konik Tipi Viskoelastik Helislerin Farklı Yüklemeler Altındaki Dinamik Davranışı

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2015Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2015Bu çalışmanın amacı, Timoshenko çubuk kuramına dayalı karışık sonlu eleman formülasyonu kullanılarak daire kesitli konik tipi doğrusal viskoelastik helislerin düzgün yayılı yük etkisinde dinamik davranışını araştırmaktır. Doğrusal viskoelastik malzemenin kayma modülü standart model ile tanımlanmış ve Poisson oranı elastik alınmıştır. Sonlu eleman çözümlemesi Laplace uzayında gerçekleştirileceği için, viskoelastik malzeme özellikleri karşıgelim ilkesi kullanılarak belirlenmiş ve. Laplace uzayında elde edilen sonuçlar, geliştirilmiş Durbin dönüşüm algoritması kullanılarak zaman uzayına taşınmıştır. Örnek problemlerde iki farklı sınır koşulu kullanılmıştır: bir ucundan tutulu diğer ucu serbest helis ve iki ucu tutulu helis. Her iki durum için adım ve impulsif tiplerinde (dikdörtgen, sinüzoidal, dik üçgen ve üçgen formlarında olmak üzere) düşeyde etkiyen dinamik yayılı yüklemeler etkisindeki helislerin dinamik davranışı incelenmiştir.The objective of this study is to investigate the dynamic behavior of a linear viscoelastic conical type helical bar having a solid circular cross-section subjected to vertical distributed loading by using the mixed finite method based on Timoshenko beam theory. It is assumed that, the linear viscoelastic material exhibits the standard type of distortional behavior while having elastic Poisson's ratio. The finite element analysis is carried out in Laplace space, the material properties are implemented into the formulation through the use of the correspondence principle. The results are transformed back to the time domain numerically by using of the Modified Durbin's transformation algorithm. Two different cases of boundary conditions are considered in the sample problems: helix fixed from one end (cantilevered) and helix fixed from two ends. For each case, the dynamic responses of the helices are determined for step and impulsive types (having rectangular, sinusoidal, right triangular and triangular forms) of dynamic vertical distributed loadings

Molecularly Imprinted Sensors — New Sensing Technologies

In this chapter we discus molecular imprinting technology (MIT), molecular imprinted polymers (MIPs), and their compatibility on a proper transducer to construct a sensing system. Molecularly imprinted sensors (MISens), in other words, artificial receptor-based sensors synthesized in the presence of the target molecule, are capable of sensing target molecules by using their specific cavities and are compatible with the target molecule. This MIP technology is a viable alternative of artificial receptor technology, and the sensor technology is capable of detecting any kind of molecule without pre-analytic preparations. In this chapter, you can find examples, sensor construction techniques and fundamentals of MIP and sensor combinations to look forward in your studies. For sensor technology, we explained and discussed the new sensing technologies of MIP-based electrochemical, optical (especially surface plasmon resonance, SPR), and piezoelectric techniques. Therefore, this chapter presents a short guideline of MISens

Fıçı Tipi Doğrusal Viskoelastik Helislerin Dinamik Davranışı

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2015Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2015Bu çalışmada, viskoelastik parametrelerin dairesel kesitli fıçı (barrel) tipi doğrusal viskoelastik helislerin dinamik davranışı üzerindeki etkileri Timoshenko çubuk kuramını esas alan bir karışık sonlu eleman algoritması kullanılarak incelenmiştir. Helisin iki ucundan tutulu ve dinamik olarak adım tipinde düzgün yayılı yük etkisinde olduğu varsayılmıştır. Doğrusal viskoelastik malzemede, kayma şekil değiştirmelerinin standart modele ve hacimsel şekil değiştirmelerinin ise Kelvin modele uygun davranış gösterdiği kabul edilmiş ve karşıgelim ilkesi kullanılarak malzeme özellikleri çözüm algoritmasına eklenmiştir. Helis probleminin çözümü Laplace uzayında gerçekleştirilmiş ve sonuçlar geliştirilmiş Durbin dönüşüm algoritması kullanılarak zaman uzayına taşınmıştır. Doğrusal viskoelastik fıçı tipi helislerin dinamik davranışına ait sayısal sonuçlar detaylı olarak irdelenmiştir.In this study, the effects of viscoelastic parameters on the dynamic behavior of a linear viscoelastic circular cross-sectioned barrel type helix is investigated by using the mixed finite element method based on the Timoshenko beam theory. The helix is assumed to be fixed from both ends and subjected to dynamic step type of vertical distributed loading. The linear viscoelastic material exhibits standard type of distortional behavior and Kelvin type of bulk compressibility, and, the material properties are implemented into the formulation through the use of the correspondence principle. The solutions of the helix problem are obtained in the Laplace space and the results are transformed back to the time domain numerically by means of the Modified Durbin's transformation algorithm. Numerical results for the dynamic behavior of linear viscoelastic barrel type helix are discussed extensively

Viskoelastik Eliptik Düzlem Çubukların Dinamik Analizi

Konferans Bildirisi-- İstanbul Teknik Üniversitesi, Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2017Conference Paper -- İstanbul Technical University, Theoretical and Applied Mechanical Turkish National Committee, 2017Bu çalışmanın amacı, Timoshenko çubuk kuramına dayalı karışık sonlu eleman formülasyonunu kullanarak, farklı sınır koşulları ve çubuk kesitlerine sahip doğrusal viskoelastik eliptik kirişlerin düzgün yayılı yük etkisinde dinamik davranışını incelemektir. Doğrusal viskoelastik malzemenin kayma modülü standart model ile tanımlanmış ve Poisson oranının elastik olduğu kabul edilmiştir. Sonlu eleman çözümleri Laplace uzayında gerçekleştirileceği için, viskoelastik malzeme özellikleri karşıgelim ilkesi kullanılarak belirlenmiş ve Laplace uzayında elde edilen sonlu eleman sonuçları, geliştirilmiş Durbin dönüşüm algoritması kullanılarak zaman uzayına taşınmıştır. Problemlerde iki farklı sınır koşulu kullanılmıştır: iki ucundan rijit tutulu ve konsol. Net alanları birbirine eşit olan farklı kesitler seçilmiştir: dairesel ve iki farklı oryantasyona sahip eliptik kesit geometrisi. Farklı sınır koşulları ve kesit türlerinin eliptik düzlem kirişin elastik ve viskoelastik davranışına olan etkisi detaylı olarak incelenerek özgün örnek olarak literatüre sunulmuştur.The objective of this study is to investigate the dynamic behavior of a linear viscoelastic elliptical beam having different types of boundary conditions and cross-sections subjected to vertical distributed loading by using the mixed finite method based on Timoshenko beam theory. It is assumed that, the linear viscoelastic material exhibits the standard type of distortional behavior while having elastic Poisson's ratio. The finite element analysis is carried out in Laplace space, the material properties are implemented into the formulation through the use of the correspondence principle. The results are transformed back to the time domain numerically by using of the Modified Durbin's transformation algorithm. Two different types of boundary conditions are considered in the problems: fixed-free, fixed-fixed. Different types of cross-sections keeping the net area equal to each other are selected: circular and two different elliptically oriented cross sections. The effect of different types of boundary conditions and cross-sections on the behavior of elastic and viscoelastic elliptical planar beam is investigated in detail and the examples are presented as original examples for the literature

Parental psychological distress associated with COVID-19 outbreak: A large-scale multicenter survey from Turkey

Aims: Pandemics can cause substantial psychological distress; however, we do not know the impact of the COVID-19 related lockdown and mental health burden on the parents of school age children. We aimed to comparatively examine the COVID-19 related the stress and psychological burden of the parents with different occupational, locational, and mental health status related backgrounds. Methods: A large-scale multicenter online survey was completed by the parents (n = 3,278) of children aged 6 to 18 years, parents with different occupational (health care workers—HCW [18.2%] vs. others), geographical (İstanbul [38.2%] vs. others), and psychiatric (child with a mental disorder [37.8%]) backgrounds. Results: Multivariable logistic regression analysis showed that being a HCW parent (odds ratio 1.79, p <.001), a mother (odds ratio 1.67, p <.001), and a younger parent (odds ratio 0.98, p =.012); living with an adult with a chronic physical illness (odds ratio 1.38, p <.001), having an acquaintance diagnosed with COVID-19 (odds ratio 1.22, p =.043), positive psychiatric history (odds ratio 1.29, p <.001), and living with a child with moderate or high emotional distress (odds ratio 1.29, p <.001; vs. odds ratio 2.61, p <.001) were independently associated with significant parental distress. Conclusions: Parents report significant psychological distress associated with COVID-19 pandemic and further research is needed to investigate its wider impact including on the whole family unit. © The Author(s) 2020

L-Fenilalanin Tayini İçin Moleküler Baskılanmış Biyosensör Hazırlanması

Phenylalanine (Phe) is an essential amino acid and it is the metabolic precursor of non-essential amino acid tyrosine and its derivatives. In the presence of phenylalanine hydroxylase (PAH), phenylalanine is converted into tyrosine. Tyrosine, therefore Phe, is used in synthesizing proteins, neurotransmitter substances (dopamine, nephrine, norepinephrine), and thyroid hormones. In this study, molecularly imprinted electrochemical biosensor was prepared to detect L-phenylalanine. Electrochemical biosensor was prepared in the presence of template (L-Phe) and functional monomer thiophene-3-carbonyl-L-tryptophan on gold electrode surface with electropolymerization. In the first step of the study, thiophene-3-carbonyl-L-tryptophan was synthesized by the reaction of 3-carboxythiophene and L-tryptophan. The results showed that the imprinted sensor has high selectivity and sensitivity for L-phenylalanine.Fenilalanin (Phe) esansiyel bir aminoasit olup esansiyel olmayan aminoasit tirozin ve türevlerinin metabolik öncülüdür. Fenilalanin, fenilalanin hidroksilaz enzimi (PAH) varlığında tirozine dönüştürülür. Tirozin, dolayısıyla Phe, protein yapımında, nörotransmitter maddelerin (dopamin, nefrin, norepinefrin) ve tiroid hormonlarının yapımında kullanılır. Bu çalışmada; L-fenilalanin tayinine yönelik moleküler baskılanmış elektrokimyasal biyosensör hazırlanmıştır. Elektrokimyasal biyosensör, kalıp molekül (L-fenilalanin) ve fonksiyonel monomer tiyofen-3-karbonil triptofan varlığında altın elektrot yüzeyinde elektriksel polimerizasyonla hazırlanmıştır. Çalışmanın ilk aşamasında, L-fenilalaninle etkileşmesi için uygun yapıda fonksiyonel monomer olarak seçilen tiyofen-3-karbonil-L-triptofan, 3-karboksitiyofen ve L-triptofanın reaksiyona sokulmasıyla sentezlenmiştir. Sonuçlar, baskılanmış sensörün L-fenilalanin için yüksek seçiciliğe ve duyarlılığa sahip olduğunu göstermektedir

İnce Ve Kalın Kutu Kesitli Helislerin Karışık Sem İle Analizi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2013Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2013Mühendislik uygulamalarında önemli görevlere hizmet eden helisel yaylar, inşaat mühendisliğinde de yaygın olarak kullanılmaktadırlar. Bu çalışmada, Timoshenko çubuk varsayımını esas alan bir fonksiyonel kullanılarak ince ve kalın cidarlı kutu kesitli elastik konik helisler karışık sonlu eleman metoduyla incelenmiştir. Kutu kesitin burulma eylemsizliği momentinin hesabında et kalınlığı ince iken kullanılan ve uygun sonuçlar veren ampirik formüller, et kalınlığı arttıkça gerçekçi sonuçlar vermekten uzaklaşmaktadır. Çözüm burulma rijitliğini Poisson denklemi üstünden elde etmek olabilir. Poisson denklemi sonlu eleman metoduyla çözülerek, kutu kesitlerin burulma rijitliği hesaplanmış, et kalınlığı ince ve kalın kesitli helis problemi ele alınarak sayısal uygulamalar üstünden burulma rijitliğinin önemi vurgulanmıştır.Helical springs which serve important tasks in engineering applications, are widely used in civil engineering. In this study, analysis of elastic conical helixes with thin and thick box shaped cross section is investigated by using the mixed finite element formulation based on Timoshenko beam theory. The empirical formulas used in the calculation of torsional inertia for thin-box section give realistic results, but diverge with increasing thickness. To overcome this problem, Poisson equation can be used. To calculate the moment of torsional inertia, Poisson equation is solved by using the finite element method and numerical examples are solved for thin and thick box sections. The importance of the torsional rigidity in the helix problems is emphasized

Free vibration of axially FG curved beam on orthotropic Pasternak foundation via mixed FEM

The main objective of this study is to present an accurate and consistent original formulation to describe the interaction between planar straight/curved beam structure and orthotropic foundation by highlighting the problematic orthotropic foundation models currently used in the literature. The proposed formulation introduces a consistent reduction of a 2D stress state of an elastic orthotropic foundation to a 1D form suitable for interaction with a beam. The formulation is also extended for curved beams resting on an arbitrarily orthotropic generalized Pasternak foundation by including a rocking effect. The beam is assumed to be made of a two-phase composite material of metal-matrix and ceramic-inclusion varying continuously through the parabolic beam axis. The effective material properties of the axially functionally graded material are predicted through a cubic local representative volume elements scheme. A two-noded curved beam element is employed based on a mixed finite element formulation based on Timoshenko beam theory by considering cross-sectional warping and the tests are performed over free vibration analyses. The new formulation of orthotropic Pasternak foundation for straight beam interaction is firstly verified by the results of a plate resting on orthotropic foundation. The flaws of existing formulations in the literature are explained, and the erroneous results produced by some of them are shown with comparison examples. The formulation is capable of modelling straight beams as well as general curved planar beams and orthotropic Pasternak foundation interaction problems. It is believed that the derived expression be safely implemented for further analyses, where beam like structures interacting with orthotropic foundation or substrate. Furthermore, this study presents free vibration results of several original benchmark examples using the mixed finite element formulation, e.g. straight and parabolic beams resting on an arbitrarily orthotropic generalized Pasternak foundation.International Technological Universit