A Two-Level Homogenization Approach for Polymer Nanocomposites with Coated Inclusions

In polymer nanocomposites, other than the matrix and inclusion, a third phase so-called interphase, is commonly observed. Inter-phase properties affect the overall macroscopic mechanical behavior. It is crucial to model the interphase and obtain the effective composite properties accordingly. Homogenization theory is very useful and powerful; however, many of the homogenization-based techniques have deficiencies. The goal of the study is to combine two very well-known homogenization techniques to model the polymer nanocomposites with coated inclusions. One of the goals of the study is to demonstrate the deficiency that originated from the interphase modeling and overcome this problem by the proposed two-level homogenization method. This method aims to model load transfer between the matrix and the reinforcement element through the interphase in a correctly. For this purpose, first, an effective inclusion is formed using finite element homogenization, then the effective inclusion and the matrix are homogenized using micromechanics-based Double Inclusion method. The proposed method provides a remarkable improvement compared to the micromechanics-based method for the soft interphase case

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

Usefulness of procalcitonin for diagnosis of sepsis in the intensive care unit

INTRODUCTION: The diagnosis of sepsis in critically ill patients is challenging because traditional markers of infection are often misleading. The present study was conducted to determine the procalcitonin level at early diagnosis (and differentiation) in patients with systemic inflammatory response syndrome (SIRS) and sepsis, in comparison with C-reactive protein, IL-2, IL-6, IL-8 and tumour necrosis factor-α. METHOD: Thirty-three intensive care unit patients were diagnosed with SIRS, sepsis or septic shock, in accordance with the American College of Chest Physicians/Society of Critical Care Medicine consensus criteria. Blood samples were taken at the first and second day of hospitalization, and on the day of discharge or on the day of death. For multiple group comparisons one-way analysis of variance was applied, with post hoc comparison. Sensitivity, specificity and predictive values of PCT and each cytokine studied were calculated. RESULTS: PCT, IL-2 and IL-8 levels increased in parallel with the severity of the clinical condition of the patient. PCT exhibited a greatest sensitivity (85%) and specificity (91%) in differentiating patients with SIRS from those with sepsis. With respect to positive and negative predictive values, PCT markedly exceeded other variables. DISCUSSION: In the present study PCT was found to be a more accurate diagnostic parameter for differentiating SIRS and sepsis, and therefore daily determinations of PCT may be helpful in the follow up of critically ill patients

Analytical and numerical methods for finite-strain elastoplasticity

An important class of finite-strain elastoplasticity is based on the multiplicative decomposition of the strain tensor $F=F_el F_pl$ and hence leads to complex geometric nonlinearities. This survey describes recent advances on the analytical treatment of time-incremental minimization problems with or without regularizing terms involving strain gradients. For a regularization controlling all of $abla F_pl$ we provide an existence theory for the time-continuous rate-independent evolution problem, which is based on a recently developed energetic formulation for rate-independent systems in abstract topological spaces. In systems without gradient regularization one encounters the formation of microstructures, which can be described by sequential laminates or more general gradient Young measures. We provide a mathematical framework for the evolution of such microstructure and discuss algorithms for solving the associated space-time discretizations. We outline in a finite-step-sized incremental setting of standard dissipative materials details of relaxation-induced microstructure development for strain softening von Mises plasticity and single-slip crystal plasticity. The numerical implementations are based on simplified assumptions concerning the complexity of the microstructures

The addition of droperidol or clonidine to epidural tramadol shortens onset time and increases duration of postoperative analgesia

Purpose: To compare tramadol alone and the combinations of either tramadol-clonidine or tramadol-droperidol with regard to analgesic and adverse effects. Methods: After Ethic's Committee approval and patient informed consent were obtained, epidural catheters were inserted preoperatively at the L3-4 interspace in 90 ASA physical status I-II adult patients undergoing lower abdominal surgery. Anesthesia was standardized. Patients were randomly assigned to one of three groups. Group I (T) patients received tramadol 75 mg, Group II (TD) patients received tramadol 75 mg plus droperidol 2.5 mg, and Group III (TC) patients received tramadol 75 mg plus clonidine 150 μg in a total volume of 10 mL administered as a single epidural injection in the postanesthesia care unit. The onset time of analgesia and duration of analgesia, visual analogue pain scores, sedation, nausea scores, vital signs and side effects were recorded. Results: Duration of analgesia was similar in both the TD and TC groups, and significantly longer than in the T group (P < 0.001). Group TC patients displayed a significant increase in sedation scores and decrease in blood pressure and heart rate when compared with other groups (P < 0.001). No adverse effects were observed in Group TD, while nausea scores were high in both the T and TC groups (P < 0.001). Pain score, respiration rate, and SpO2 values were similar in all study groups. Conclusion: We conclude that epidural tramadol in combination with droperidol or clonidine prolongs the duration of analgesia; however, droperidol appears to be a better alternative when adverse effects and antiemetic properties are taken into consideration

Comparative evaluation of two different volumes of lidocaine in intravenous regional anesthesia

Background: This study was conducted to compare low concentration-high volume intravenous regional anesthesia (IVRA) method with local anesthetic method in upper extremity surgery in terms of efficiency and adverse effects. Material/Methods: Thirty-nine patients were divided into 2 groups; the first group received a 2% concentration of 12-15 mL lidocaine (Group 1) and the second group received a 0.5% concentration of 30-50 mL lidocaine (Group 2). Intraoperative hemodynamic data of patients (systolic blood pressure, diastolic blood pressure, mean blood pressure, heart rate, and peripheral oxygen saturation- SpO2) was recorded before and after anesthesia at 1, 5, 10, 15, 20, and 40 minutes. Results: The intergroup and intragroup comparisons did not reveal any significant differences in hemodynamic data. The onset time of sensorial block was shorter and the regression time of sensorial block was longer in Group 1 than Group 2. Group 1 had shorter onset time of motor block and longer regression time of motor block than Group 2. There were no significant differences between the study groups in terms of the time of tourniquet and postoperative analgesia time. Conclusions: IVRA technique applied with 2% concentration and volume of 12-15 mL lidocaine may be suggested as a safe option. © Med Sci Monit, 2013

KOMPLEKS VE KOMPOUND ODONTOMA, 22 VAKA SUNUMU

Amaç Odontomalar çenelerde en sık görülen odontojenik kökenli iyi huylu tümörlerdir. Yavaş büyürler ve agresif davranış göstermezler. Genellikle asemptomatiktirler ve sıklıkla rutin radyografi sırasında bulunurlar. Kompleks ve kompaund odontoma olarak ikiye ayrılmaktadır. Bu vaka serisinde 8’i komplex 14'ü kompaund, toplam 22 odontoma vakasının cerrahi tedavisinin anlatılması amaçlanmıştır. Olgular Sunumu Yaş aralığı 10-34 arası olan 14’ü kadın 8’i erkek toplam 22 hasta, bölümümüzde gerekli klinik ve radyolojik muayenelerden sonra cerrahi olarak opere edilmiştir. Çıkarılan dokuların histopatalojilerinin, radyolojik ve klinik bulgularla değerlendirilmesi ile 8’inin komplex 14’ünün kompound odontoma olduğu tespit edilmiştir. Bazı vakalarda odontoma ile birlikte gömülü diş alınırken bazı vakalarda diş sürmesinin takibi amacıyla veya çene fraktürü riski sebebiyle etken gömülü dişler bırakılmıştır. İyileşme süresince hastalarda herhangi bir komplikasyon görülmemiştir. Sonuç Odontomalar genellikle asemptomatik görüldükleri için hastaların diş hekimlerine rutin kontrollere gelmeleri, erken teşhiste çok önemlidir. Erken teşhis ile morbidite ve maliyet azaltılabilir

Aspekte der Energieminimierung in der Festkörpermechanik : Entwicklung inelastischer Mikrostrukturen und Rißausbreitung

This work deals with theoretical energy minimization principles and the development of associated computational tools for the description of microstructure evolution and fracture in solid mechanics. The thesis consists of two parts: (i) The description of inelastic deformation microstructures and their evolution in non-convex unstable solids and (ii) the development of a variational framework for configurational-force-driven brittle fracture based on energy minimization principles. In the first part, a general framework is developed for the treatment of material instabilities and microstructure developments in inelastic solids. Material instabilities and microstructure developments are interpreted as the outcome of non(quasi)-convex variational problems which often suffer from the lack of solutions in the classical sense. The proposed framework is based on a mathematical relaxation theory which is associated with the replacement of non-quasiconvex potentials with their generalized convex envelopes. Furthermore, deformation microstructures and their evolution are studied for three different constitutive material responses: the symmetry-breaking martensitic phase transformations, the single-slip crystal plasticity and the isotropic damage mechanics. For this purpose specific numerical relaxation algorithms are proposed for each constitutive response. The performance of numerical relaxation schemes is presented by several representative examples. In the second part, a variational formulation of quasistatic brittle fracture in elastic solids is outlined and a finite-element-based computational framework is proposed for the two- and three-dimensional crack propagation. The starting point is a variational setting that recasts a monotonic quasistatic fracture process into a sequence of incremental energy minimization problems. The proposed numerical implementation exploits this variational structure. It introduces discretized crack patterns with configurational-force-driven incremental crack segment and crack surface releases. These releases of crack segments and surfaces constitute a sequence of positive definite subproblems with successively decreasing overall stiffness, providing an extremely robust algorithmic setting in the postcritical range. The formulation is embedded into an accompanying r-adaptive crack-pattern adjustment procedure with configurational-force-based indicators in conjunction with crack front constraints. The performance of the proposed algorithm is demonstrated by means of several two- and three-dimensional crack propagation examples and comparisons with experiments.Die Arbeit befaßt sich mit Theorie und Numerik der Entwicklung von Mikrostrukturen und Bruch in der Festkörpermechanik. Sie besteht aus zwei Teilen: (i) Beschreibung von inelastischen Deformationsmikrostrukturen und ihrer Evolution in nichtkonvexen instabilen Körpern und (ii) Entwicklung einer Variationsformulierung für konfigurationskraftgetriebenen spröden Bruch basierend auf Energieminimierungprinzipien. Im ersten Teil wird eine allgemeine Struktur für die Behandlung von materiellen Instabilitäten und Mikrostrukturentwicklungen in inelastischen Körpern entwickelt. Materielle Instabilitäten und Mikrostrukturentwicklungen werden als Resultate nicht-(quasi)-konvexer Variationsprobleme gedeutet, für die häufig keine klassichen Lösungen existieren. Die vorgeschlagene Methodik basiert auf einer mathematischen Relaxierungstheorie, bei der die nicht-(quasi)-konvexen Potentiale durch ihre generalisierten konvexen Hüllen ersetzt werden. Außerdem werden Deformationsmikrostrukturen und ihre Entwicklung für drei unterschiedliche Klassen von Materialverhalten analysiert: symmetriebrechende martensitische Phasenumwandlungen, Kristallplastizität und isotrope Bruchmechanik. Zu diesem Zweck werden spezifische numerische Relaxierungsalgorithmen für jede der erwähnten Klassen von Materialverhalten vorgeschlagen. Die Leistungsfähigkeit der numerischen Relaxierungsmethoden wird durch einige repräsentative Beispiele dargestellt. Im zweiten Teil wird eine Variationsformulierung für quasistatischen spröden Bruch in elastischen Körpern behandelt und ein auf der Methode der Finiten Elemente basierender Ansatz für die zwei- und dreidimensionale Rißausbreitung vorgeschlagen. Ausgangspunkt ist eine Variationsstruktur, die einen monotonen quasistatischen Bruchprozeß als eine Folge inkrementeller Energieminimierungsprobleme darstellt. Die vorgeschlagene numerische Implementierung nutzt diese Variationsstruktur aus. Auf diese Weise werden diskrete Rißmuster durch die konfigurationskraftgetriebene Ausbreitung von Rißsegmenten und Rißoberflächen erzeugt. Das Entstehen von Rißsegmenten und -oberflächen stellt eine Folge positiv definiter Teilprobleme mit sukzessiv abnehmender Gesamtsteifigkeit dar, was zu einem extrem robusten Algorithmus im postkritischen Bereich führt. Die Formulierung ist außerdem in ein r-adaptives Verfahren zur Anpassung des Rißmusters mit konfigurationskraftbasierten Indikatoren und Zwangsbedingungen durch die Rißfront eingebettet. Die Leistungsfähigkeit des vorgeschlagenen Algorithmus wird anhand einiger zwei- und dreidimensionaler Rißausbreitungsbeispiele und dem Vergleich mit Experimenten demonstriert