A higher order control volume based finite element method to prodict the deformation of heterogeneous materials

Materials with obvious internal structure can exhibit behaviour, under loading, that cannot be described by classical elasticity. It is therefore important to develop computational tools incorporating appropriate constitutive theories that can capture their unconventional behaviour. One such theory is micropolar elasticity. This paper presents a linear strain control volume finite element formulation incorporating micropolar elasticity. Verification results from a micropolar element patch test as well as convergence results for a stress concentration problem are included. The element will be shown to pass the patch test and also exhibit accuracy that is at least equivalent to its finite element counterpart

Deoxyribonucleic Acid as a Universal Electrolyte for Bio-Friendly Light-Emitting Electrochemical Cells [in press]

In the search for bio and eco‐friendly light sources, light‐emitting electrochemical cells (LECs) are promising candidates for the implementation of biomaterials in their device architecture thanks to their low fabrication complexity and wide range of potential technological applications. In this work, the use of the DNA derivative DNA‐cetyltrimethylammonium (DNA‐CTMA) is introduced as the ion‐solvating component of the solid polymer electrolyte (SPE) in the active layer of solution‐processed LECs. The focus is particularly on the investigation of its electrochemical and ionic conductivity properties demonstrating its suitability for device fabrication and correlation with thin film morphology. Furthermore, upon blending with the commercially available emissive polymer Super Yellow, the structure property relationship between the microstructure and the ionic conductivity is investigated and yields an optimized LEC performance. The large electrochemical stability window of DNA‐CTMA enables a stable device performance for a variety of emitters covering the complete visible spectral range, thus highlighting the universal character of this naturally sourced SPE

Investigation of indentation and dry sliding wear behaviour of Al-12.6 wt.% Si-10 wt.% TiB2 composites produced by sequential milling and pressureless sintering

The main purpose of this study is to comprehend the effects of cryomilling (CM) time on dry sliding wear behaviour of 10 wt.% TiB2 reinforced Al-12.6 wt.% Si metal matrix composites (MMCs). The MMCs were synthesised via sequential milling (mechanical alloying + cryomilling) and pressureless sintering. Indentation tests performed at a maximum load of 200 g showed that the Young's modulus and hardness of the composites increased up to 20 min of CM time. The effects of CM time and load on the composites were examined based on their tribological properties. Based on the results, the 4 h mechanical alloyed (MA'd) and 30 min CM'd sample showed the lowest wear rate under the normal load of 1 N, with its wear mechanism being predominantly oxidative. However, for the normal load of 4 N, the lowest wear rate was found in the 4 h MA'd composite, in which the dominant wear mechanism was abrasion.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [214M093]This study was carried out within the scope of the project with a number of 214M093, which was financed by The Scientific and Technological Research Council of Turkey (TUBITAK)

Sustainable Materials and Process Techniques for Engineering Solution-Based Organic Light-Emitting Devices

Advances in organic light emitting devices are crucial for the development of the display and solid state lighting (SSL) technologies. This dissertation is organized and pursued in three main projects to meet some problems in the field. Printing technologies can be the key to next-generation affordable, flexible, large area displays and lighting elements by eliminating vacuum processing. In the first part of the thesis, the conventional gravure printing technique was adapted for the processing of emissive layers in the small molecule based organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs). The homogeneous printed layers were granted by either modifying the functional ink properties or altering the printing process parameters. Different functional inks comprising the small molecule as an emissive material were formulated by adjusting viscosity, surface tension, and solvent drying kinetics of the inks. As for the process parameters, the gravure cell parameters such as line screen and tone values were altered to control the overall transfer volume of the ink and the thickness of the printed layers. In both cases, the electrically inert polymers were used as host materials to modify the rheological behavior of the ink while suppressing the aggregation of the small molecule in a solid film. The thin film characteristics of printed layers were analyzed in both qualitative and quantitative ways. The printed films were successfully implemented in the active layer of efficient small molecule based electroluminescent devices on flexible plastic foil. The optical and electrical device performance were considered as well as the effect of the printing process in comparison to spin-coated pristine small molecule based reference devices. The quality and performance of the printed emissive layers in both device type showed that the gravure printing method can be an alternative solution for wet-processing roll-to-roll (R2R) manufacturing in the future. White light-emitting diodes draw particular attention in the field, due to their potential application as the backlight in displays or as energy efficient luminaires for SSL. Even though polymer OLEDs are well-suited for wet-based continues R2R fabrication, evaporation of low work function cathodes and therewith encapsulation remain as major obstacles. In the second part of the work, a novel hybrid device architecture was suggested for the color-tuning and white light emission in polymer light-emitting diodes. The single component polymer LEC layer performed as the electron injection layer as well as the second emissive layer on top of a conventional polymer OLED stack. The hybrid structure maintained a sufficient charge carrier injection from an air-stable cathode, due to the unique operation principles of LECs. As a proof of charge transport at the intersection of two emissive layers, dual color emission was simultaneously observed in a bilayer device configuration. A color-tuning in emission was obtained by changing the thickness of the LEC layer. The emission of hybrid devices was shifted from yellow to white light emission region of the CIE color chromaticity diagram, resulting in OLEDs with the high color temperature values. The results demonstrated that this approach showed a promising potential to achieve color-tuning and white light emission from solution processed OLEDs bearing air-stable cathodes. Sustainable bioelectronics is an emerging technology which to replace conventional electronics with disposable counterparts in the future. Thus, bioinspired and bioderived materials usage in organic electroluminescent devices gained much attention in the last years. In the last part of the thesis, we investigated biodegradable natural and naturally derived polymers such as gelatin, deoxyribonucleic acid (DNA) as the ion-solvating polymers in the emissive layer of polymer LECs. Notably, we focused on DNA and DNA-lipid complex based polyelectrolytes due to the unique hybrid ionic/electronic conductivity behavior of DNA. Different solid polymer electrolytes (SPE) were tested with varying additives of salts at different ratios towards improving the ionic conductivity. Additionally, the electrochemical stability window of SPEs was defined to eliminate nonreversible electrochemical side reactions during device operation. The optoelectrical device characteristics, as well as lifetime measurements, were obtained to determine the stability of LECs. Furthermore, the surface morphology of the active layers was investigated to characterize the phase separation between SPE and emissive polymer and aggregations in thin films, which have a significant influence on the device performance. Biosolid polymer electrolytes were successfully implemented in LECs as promising materials of bio-based LECs

Sustainable Materials and Process Techniques for Engineering Solution-Based Organic Light-Emitting Devices

Advances in organic light emitting devices are crucial for the development of the display and solid state lighting (SSL) technologies. This dissertation is organized and pursued in three main projects to meet some problems in the field. Printing technologies can be the key to next-generation affordable, flexible, large area displays and lighting elements by eliminating vacuum processing. In the first part of the thesis, the conventional gravure printing technique was adapted for the processing of emissive layers in the small molecule based organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs). The homogeneous printed layers were granted by either modifying the functional ink properties or altering the printing process parameters. Different functional inks comprising the small molecule as an emissive material were formulated by adjusting viscosity, surface tension, and solvent drying kinetics of the inks. As for the process parameters, the gravure cell parameters such as line screen and tone values were altered to control the overall transfer volume of the ink and the thickness of the printed layers. In both cases, the electrically inert polymers were used as host materials to modify the rheological behavior of the ink while suppressing the aggregation of the small molecule in a solid film. The thin film characteristics of printed layers were analyzed in both qualitative and quantitative ways. The printed films were successfully implemented in the active layer of efficient small molecule based electroluminescent devices on flexible plastic foil. The optical and electrical device performance were considered as well as the effect of the printing process in comparison to spin-coated pristine small molecule based reference devices. The quality and performance of the printed emissive layers in both device type showed that the gravure printing method can be an alternative solution for wet-processing roll-to-roll (R2R) manufacturing in the future. White light-emitting diodes draw particular attention in the field, due to their potential application as the backlight in displays or as energy efficient luminaires for SSL. Even though polymer OLEDs are well-suited for wet-based continues R2R fabrication, evaporation of low work function cathodes and therewith encapsulation remain as major obstacles. In the second part of the work, a novel hybrid device architecture was suggested for the color-tuning and white light emission in polymer light-emitting diodes. The single component polymer LEC layer performed as the electron injection layer as well as the second emissive layer on top of a conventional polymer OLED stack. The hybrid structure maintained a sufficient charge carrier injection from an air-stable cathode, due to the unique operation principles of LECs. As a proof of charge transport at the intersection of two emissive layers, dual color emission was simultaneously observed in a bilayer device configuration. A color-tuning in emission was obtained by changing the thickness of the LEC layer. The emission of hybrid devices was shifted from yellow to white light emission region of the CIE color chromaticity diagram, resulting in OLEDs with the high color temperature values. The results demonstrated that this approach showed a promising potential to achieve color-tuning and white light emission from solution processed OLEDs bearing air-stable cathodes. Sustainable bioelectronics is an emerging technology which to replace conventional electronics with disposable counterparts in the future. Thus, bioinspired and bioderived materials usage in organic electroluminescent devices gained much attention in the last years. In the last part of the thesis, we investigated biodegradable natural and naturally derived polymers such as gelatin, deoxyribonucleic acid (DNA) as the ion-solvating polymers in the emissive layer of polymer LECs. Notably, we focused on DNA and DNA-lipid complex based polyelectrolytes due to the unique hybrid ionic/electronic conductivity behavior of DNA. Different solid polymer electrolytes (SPE) were tested with varying additives of salts at different ratios towards improving the ionic conductivity. Additionally, the electrochemical stability window of SPEs was defined to eliminate nonreversible electrochemical side reactions during device operation. The optoelectrical device characteristics, as well as lifetime measurements, were obtained to determine the stability of LECs. Furthermore, the surface morphology of the active layers was investigated to characterize the phase separation between SPE and emissive polymer and aggregations in thin films, which have a significant influence on the device performance. Biosolid polymer electrolytes were successfully implemented in LECs as promising materials of bio-based LECs

Evaluation of Clinical Data Management Systems for Investigator Initiated Trials

Durch den Einsatz von Web- und Informationstechnologien können die Abläufe in klinischen Studien optimiert, die Datenqualität erhöht und die Kosten reduziert werden. Um die Durchführung von klinischen Studien im akademischen bzw. universitären Bereich zu unterstützen, soll an der Medizinischen Universität Wien ein Clinical Data Management System (CDMS) zum Einsatz kommen. Das CDMS soll die neuesten technischen Entwicklungen und Standards unterstützen sowie die Benutzeranforderung im Rahmen der Studienprozesse erfüllen.Das Ziel dieser Arbeit ist die funktionalen Anforderungen an ein CDMS aus Sicht der Benutzer zu erheben, die Evaluierung von ausgewählten CDMS durchzuführen und eine Systemauswahl zu argumentieren.Für die Anforderungserhebung wurden die Studienprozesse anhand von UML Diagrammen modelliert. Basierend auf den Anwendungsfall- und Aktivitätsdiagrammen wurden die funktionalen Anforderungen generiert und in einem Kriterienkatalog strukturiert abgebildet. Anhand dieses Kriterienkatalogs wurde die Evaluierung von drei ausgewählten Systemen (MARVIN von XClinical, EDC System des AIT und OpenClinica von Akaza Research) durchgeführt. Die Anforderungen wurden je nach Erfüllungsgrad bewertet. Anschließend wurde eine Systemauswahl argumentiert. Während der Evaluierung standen die Systeme mit jeweils unterschiedlichen Funktionsumfängen zur Verfügung. Das EDC System des AIT wurde von der Systemauswahl aufgrund der hohen Anzahl von nicht erhebbaren Anforderungen ausgeschlossen. Der Einsatz von MARVIN und OpenClinica im Rahmen von akademischen klinischen Studien kann empfohlen werden. Beide Systeme erfüllen die Anforderungen ohne wesentliche Unterschiede.Unterschiede liegen im Erfüllungsgrad des Prozessablaufes vor. Zur Entscheidungsfindung wird eine zusätzliche Evaluierung der Prozessunterstützung in den jeweiligen Systemen empfohlen.To support academic researchers conducting Investigator Initiated Trials (IITs), a Clinical Data Management System (CDMS) should be established at the Medical University of Vienna. The use of information and web technologies can optimize the clinical trial processes, increase the data quality and reduce costs. The CDMS should support the latest technological developments and standards, and satisfy the user requirements in accordance with the trial processes.The aim of this work is to specify the functional user requirements, to evaluate existing CDMS and to argument the selection of a CDMS. To specify the requirements for a CDMS, the clinical trial processes were modeled using UML use case diagrams and activity diagrams. Based on these UML Diagrams the functional requirements were generated and represented in a structured way - in a criteria catalog. This criteria catalog (including the requirements) was used to evaluate three selected CDMS (MARVIN from XClinical, EDC System from AIT and OpenClinica from Akaza Research). The requirements have been assessed according to the compliance level for each system. Subsequently a system selection was argued. Each system was provided at a different level of available functions. The EDC system of the AIT was excluded from the system selection process because of the high number of non answerable requirements. The use of MARVIN and OpenClinica in conducting academic clinical trials can be recommended. Both systems satisfy the requirements without major differences. They differ in the level of process compliance. For choosing a system, the comparison of the compliance of the supported processes in each system is recommended

Unit Cell Calculations Under Fully Characterized Stress States

The available numerical methods for performing finite element unit cell calculations under stress states evolving in a predefined manner restrict the most general stress state to a single shear stress component superimposed on three normal stress components. The present study builds on and extends state of the art such that the behavior of a unit cell under the most complex stress states, comprising three shear and three normal stress components, can be explored. The proposed method is implemented in the commercial finite element software Abaqus. Three-dimensional cubic unit cells containing either a void or a particle at the center and subjected to various stress states showed that the developed method is accurate and computationally efficient. Furthermore, simulations using voided unit cells demonstrate that ductile failure is an anisotropic process, with anisotropy intensifying in the presence of shear loads. That is, void growth and strain localization leading to ductile fracture are influenced by the relative ratios of all shear stress components as well as the stress triaxiality and the Lode parameter