Yarı Kristal Polimer Malzemelerin Çok Ölçekli Modellenmesi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2013Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2013Bu çalışmada iki fazlı yarı kristal polimerik malzemeler için geometrik olarak doğrusal olmayan, mikromekaniksel motivasyonlu ve çok ölçekli bir malzeme modeli geliştirilmiştir. Bu amaç doğrultusunda, amorf ve kristal fazlar için en önemli şekil değiştirme mekanizmaları belirlenmiş ve bu bilgi ışığında her iki faz için ayrı ayrı mikromekaniksel motivasyonu bulunan malzeme modelleri kullanılmıştır. Ardından, iki fazlı yapıyı homojenleştirerek yarı kristal polimer malzemenin makroskopik davranışını betimleyecek bir model geliştirilmiştir.In this paper a geometrically non-linear micromechanically-motivated multi-scale model is developed for two phase semi-crystalline polymeric materials. To this end, most important deformation mechanisms of amorphous and crystalline phases are determined; and in the light of this information, micromechanically-motivated material models are employed separately for both phases. Afterwards, by homogenization of the two-phase structure, , a model that would render the macroscopic response of the semi crystalline polymeric material is developed

An example of secondary fault activity along the North Anatolian Fault on the NE Marmara Sea Shelf, NW Turkey

Seismic data on the NE Marmara Sea Shelf indicate that a NNE-SSW-oriented buried basin and ridge system exist on the sub-marine extension of the Paleozoic Rocks delimited by the northern segment of the North Anatolian Fault (NS-NAF), while seismic and multi-beam bathymetric data imply that four NW-SE-oriented strike-slip faults also exist on the shelf area. Seismic data indicate that NW-SE-oriented strike-slip faults are the youngest structures that dissect the basin-ridge system. One of the NW-SE-oriented faults (F1) is aligned with a rupture of the North Anatolian Fault (NAF) cutting the northern slope of the Cinarcik Basin. This observation indicates that these faults have similar characteristics with the NS-NAF along the Marmara Sea. Therefore, they may have a secondary relation to the NAF since the principle deformation zone of the NAF follows the Marmara Trough in that region. The seismic energy recorded on these secondary faults is much less than that on the NAF in the Marmara Sea. These faults may, however, produce a large earthquake in the long term

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe

Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat

Correction to: Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

The original version of this article unfortunately contained a mistake

Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study

Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9–27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6–16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2–1.8), stage II (OR 1.6; 95% CI 1.4–1.9), and stage III or worse (OR 2.8; 95% CI 2.3–3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat

Modeling of spherulite microstructures in semicrystalline polymers

Semicrystalline polymers are composed of crystalline structures together with amorphous polymer chain networks and therefore they exhibit deformation mechanisms of both crystalline materials and amorphous polymers. One of the most common microstructures observed in semicrystalline polymers is the spherulite microstructure in which crystalline lamellae are embedded in a matrix of amorphous material and grow out from a common central nucleus in radial directions. The mechanical behavior of semicrystalline polymers is strongly dependent on the underlying spherulite microstructure. Therefore, characterization of the deformation of spherulites is very important to understand the mechanical behavior of semicrystalline polymers. In this work, we propose a new FEM-based model for semicrystalline polymers which explicitly discretizes the spherulite microstructure consisting of crystalline and amorphous phases. In the model, a viscoplastic crystal plasticity model is employed for the crystalline phase, whereas 8-chain model is employed for the amorphous phase. The model captures the evolution of inhomogeneous plastic deformation activity in a spherulite microstructure, as well as the important features of the spherulite deformation reported in the literature

Ultra yüksek moleküler ağırlıklı polietilenin çok ölçekli modellenmesi

TÜBİTAK MAG01.11.2014Bu projede yarı-kristal polimerler için mikromekaniksel temellere dayalı çok ölçekli malzeme modeli geliştirildi. Projenin Mayıs 2012 – Kasım 2012 arasındaki ilk döneminde iki fazlı bir yapıya sahip olan UYMAPE’in her bir fazı için farklı malzeme modellerinin üzerinde çalışıldı. Bu çlaışmanın neticesinde UYMAPE’in amorf fazı için mikro-küre modelinin, kristal fazı için ise kristal viskoplastisitesi modelinin kullanımına karar verildi. Bir sonraki Kasım 2012 – Mayıs 2013 döneminde her bir fazın bünye denklemleri ABAQUS sonlu elemanlar yazılımına UMAT altprogramı olarak kodlandı. Bu dönemde ayrıca iki fazlı yapının ortalama mekanik davranışını hesaplayacak Taylor tipi bir homojenleştirme yöntemi üzerinde çalışıldı. Mayıs 2013 – Kasım 2013 tarihleri arasındaki üçüncü dönemde ise yarı kristal polimerlerde gözlemlenen küresel mikro-yapıyı dikkate alan bir homojenleştirme yöntemi teorik olarak geliştirildi. Bu çalışmaya paralel olarak idealize edilmiş iki fazlı bir küresel yapı farklı yükleme koşulları altında doğrudan sonlu elemanlar yöntemi ile analiz edildi. Projenin Kasım 2013 – Mayıs 2014 arasındaki dördüncü döneminde bir önceki dönemde teorik altyapısı hazırlanmış olan homojenleştirme yöntemi kodlandı. Projenin Mayıs 2014 – Kasım 2014 arasındaki en son döneminde ise kodlanan homojenleştirme yönteminin istenen verimde çalışmamasından dolayı literatürden UYMAPE malzemesi için önerilmiş bir malzeme modeli bulundu ve bu model ABAQUS sonlu elemanlar yazılımına UMAT altprogramı olarak kodlandı. Daha sonra bu model ile diz eklemindeki yükleme durumuna benzer sürtünme koşullarında sonlu eleman analizleri yapıldı. Son olarak UYMAPE implantın yüzeyinde yüzey dokuları kullanılarak makroskopik sürtünme katsayısının düşürülmesine yönelik çalışmalar yapıldı.In this project, a micromechanically-based multi-scale material model has been developed for semi-crystalline polymers. In the first period of the project between May 2012 – November 2012, studies on the material models for indivudal phases of UHMWPE (ultra high molecular weight polyethylene) have been conducted and the constitutive equations to be used for individual phases have been determined. It has been decided to use the micro-sphere model for the amorphous phase and the crytal viscoplasticity for the crystalline phase. In the next period, between November 2012 – May 2013, the constitutive models for the individual phases have been implemented to ABAQUS software as UMAT subroutines. Furthermore, in this period, a Taylor-type homogenization scheme for the homogenized mechanical response of two-phase micro-structure of UHMWPE has been studied. In May 2013 – November 2013 period of the project, a homogenization approach that takes into account the spherulite micro-structure of UHMWPE has been theoretically developed. In parallel with this work, an idelaized two-phase spherulite microstructure has been discretized with finite elements and analyzed under different loading conditions. The homogenization scheme developed in the previous period has been implemented in November 2013 – May 2014 period of the project. In the last period, between May 2014 – November 2014 a constitutive model for UHMWPE has been found from the literature and implemented into ABAQUS as a UMAT subroutine due to poor performance of the developed homogenization scheme. Later finite element analyses of a model problem having loading conditions similar to knee joint have been conducted using this material model of UHMWPE. Finally, studies to reduce the macroscopic friction coefficient of UHMWPE implants by using surface texture effects have been conducted