A novel CAD algorithm for the analysis of printed geometries

Ankara : Department of Electrical and Electronics Engineering and Institute of Engineering and Science, Bilkent Univ., 1997.Thesis (Ph.D.) -- Bilkent University, 1997.Includes bibliographical refences.An efficient and accurate computer aided design (CAD) software for the electromagnetic simulation of passive microwave components, fabricated in planar stratified media, is developed in this work. The numerical technique employed in this software is based on the spatial-domain method of moments (MoM) in conjunction with the closed-form Green’s functions. Since the computational efficiency is a major issue in CAD softwares, the spatial-domain MoM is significantly improved in this respect with the use of the closed-form Green’s functions and closed-form expressions for the MoM matrix entries. Vertical metalizations in the form of via holes and shorting pins, which are the indispensable parts of the most microwave circuits, are also modeled very efficiently and incorporated into this formulation. The resulting approach is applied to some realistic microwave circuits and planar antennas, with and without vertical metalizations, to validate the formulation. It is also demonstrated that the formulation developed in this work can be efficiently used with an optimization algorithm for design purposes. The results obtained from the formulation proposed in this work are compared to those obtained from a commercial electromagnetic analysis software.Kınayman, NoyanPh.D

Ultra-sensitive bioelectronic transducers for extracellular electrophysiological studies

Extracellular electrical activity of cells is commonly recorded using microelectrode arrays (MEA) with planar electrodes. MEA technology has been optimized to record signals generated by excitable cells such as neurons. These cells produce spikes referred to as action potentials. However, all cells produce membrane potentials. In contrast to action potentials, electrical signals produced by non-excitable or non-electrogenic cells, do not exhibit spikes, rather smooth potentials that can change over periods of several minutes with amplitudes of only a few microvolts. These bioelectric signals serve functional roles in signalling pathways that control cell proliferation, differentiation and migration. Measuring and understanding these signals is of high priority in developmental biology, regenerative medicine and cancer research. The objective of this thesis is to fabricate and characterise bioelectronic transducers to measure in vitro the bioelectrical activity of non-electrogenic cells. Since these signals are in the order of few microvolts the electrodes must have an unrivaled low detection limit in the order of hundreds of nanovolts. To meet this challenge a methodology to analyze how bioelectrical signals are coupled into sensing surfaces was developed. The methodology relies on a description of the sensing interface by an equivalent circuit. Procedures for circuit parameter extraction are presented. Relation between circuit parameters, material properties and geometrical design was established. This knowledge was used to establish guidelines for device optimization. The methodology was first used to interpret recordings using gold electrodes, later it as extended to conducting polymers surfaces (PEDOT:PSS ) and finally to graphene electrolyte-gated transistors. The results of this thesis have contributed to the advance of the knowledge in bioelectronic transducers in the following aspects: (i) Detection of signals produced by an important class of neural cells, astrocyte and glioma that thus far had remained inaccessible using conventional extracellular electrodes. (ii) Development of an electrophysiological quantitative method for in vitro monitoring of cancer cell migration and cell-to-cell connections. (iii)An understanding of the limitations of electrolyte-gated transistors to record high frequency signals.A atividade elétrica extracelular das células é geralmente medida usando matrizes de micro-elétrodos (MEA) planares. A tecnologia MEA foi otimizada para medir sinais gerados por células excitáveis, como os neurónios. Essas células produzem sinais conhecidos como potenciais de ação. No entanto, todas as células produzem potenciais de membrana. Em contraste com os potenciais de ação, os sinais elétricos gerados por células não excitáveis ou não eletrogénicas, não são “spikes”, mas sinais que variam lentamente e que podem mudar ao longo de períodos de vários minutos com amplitudes de apenas alguns microvolts. Estes sinais desempenham funções importantes nos mecanismos de sinalização que controlam a proliferação, a diferenciação e a migração celular. Medir e entender esses sinais é importante na biologia do desenvolvimento, na medicina regenerativa e no desenvolvimento de novas terapias para combater células cancerosas. O objetivo desta tese é fabricar e caracterizar transdutores para medir in vitro a atividade de células não eletrogénicas. Como esses sinais são da ordem de alguns microvolts, os elétrodos devem ter um limite de detecção na ordem de centenas de nanovolts. Para enfrentar este desafio, foi desenvolvida uma metodologia para analisar a forma como os sinais se acoplam à superfície do sensor. A metodologia baseia-se na descrição da interface de detecção por um circuito eléctrico equivalente. Procedimentos para extração dos parâmetros de circuito e a relação com as propriedades do material e o desenho geométrico foi estabelecida. Este conhecimento foi usado para estabelecer diretrizes para otimização dos transdutores. Em primeiro lugar a metodologia foi usada para interpretar as medidas de sinais usando elétrodos de ouro, posteriormente estendida para analisar superfícies de polímeros condutores (PEDOT: PSS) e, finalmente, para compreender o funcionamento de transístores. Os resultados desta tese contribuíram para o avanço do conhecimento em transdutores bioeletrónicos nos seguintes aspectos: (i) Detecção de sinais produzidos por uma importante classe de células neurais, astrócitos e gliomas, que tem permanecido inacessíveis usando elétrodos extracelulares. (ii) Desenvolvimento de um método eletrofisiológico para medir a migração de células cancerosas e o estabelecimento de conexões entre células. (ii) Estudo das limitações dos transístores para medir sinais eletrofisiológicos rápidos.The work developed in this thesis was carried out within the framework of the project entitled: “Implantable Organic Devices for Advanced Therapies (INNOVATE)”, ref. PTDC/EEI-AUT/5442/2014, financed by Fundação para a Ciência e Tecnologia (FCT).This project was carried out at the laboratories of the “ Instituto de Telecomunicações (IT) UID/Multi/04326/2013” at the University of the Algarve. The PhD study period received full scholarship under European EM program, “Erasmus Mundus Action 2 (EMA2)” coordinated by University of Warsaw

Advanced Space Nuclear Reactors from Fiction to Reality

AbstractThe advanced nuclear power sources are used in a large variety of science fiction movies and novels, but their practical development is, still, in its early conceptual stages, some of the ideas being confirmed by collateral experiments. The novel reactor concept uses the direct conversion of nuclear energy into electricity, has electronic control of reactivity, being surrounded by a transmutation blanket and very thin shielding being small and light that at its very limit may be suitable to power an autonomously flying car. It also provides an improved fuel cycle producing minimal negative impact to environment. The key elements started to lose the fiction attributes, becoming viable actual concepts and goals for the developments to come, and on the possibility to achieve these objectives started to become more real because the theory shows that using the novel nano-technologies this novel reactor might be achievable in less than a century

Thermal stability and mechanical property of polymer layered graphite oxide composites

Polymer composites formed from layered fillers with high surface volume ratio show enhanced reinforcement. Graphite oxide is a high modulus material that can be separated into thin layers with high surface area. The aim of this study is to prepare polymer layered graphite oxide composites using functionalised polyolefin to enhance compatibility with various forms of layered graphite oxide in varying concentration. Functionalised polyolefins reinforced with layered graphite oxides and expanded graphite oxides were prepared using solution blending and melt blending methods. Three different mixing methods with varying shear intensity were employed to prepare polymer layered graphite oxide composites. The crystalline structure, thermal and mechanical properties of the prepared polymer layered graphite oxide composites was studied. Oxidised graphite prepared from the Staudenmaier method and its exfoliated form were dispersed in poly(ethylene-co-methyl acrylate-co-acrylic acid) (EMAA) via solution blending to prepare EMAA layered composites. The thermal stability was determined using thermogravimetric analysis. The EMAA layered composites showed higher thermal stability in comparison with pure EMAA. The mechanical properties of these EMAA layered composites were determined through dynamic mechanical analysis. Shear modulus, yield stress and storage modulus of EMAA in the presence of graphite oxide fillers decreased. A solution blending method was used to prepare poly(propylene-grafted-maleic anhydride) layered expanded graphite oxide composites (PPMA-EGO). Two types of PPMA-EGO were prepared using different mixing methods - low and high shear were employed. The effects of preparative mixing methods on the PPMA-EGO properties were investigated. The mechanical properties of PPMA-EGO obtained from dynamic mechanical analysis indicated that EGO had a reinforcing effect on the elastic behaviour of PPMA-EGO. This is due to strong interfacial adhesion between PPMA and EGO as a result of hydrogen bonding. The elastic behaviour of PPMA-EGO was affected by the surface area of graphite flakes. Low sheared PPMA-EGO elastic behaviour was found to be higher compared with that of high sheared PPMA-EGO. A melt blending method was used to prepare PPMA-EGO with varying EGO concentration. The interconnected network structure of EGO in the PPMA-EGO was not observed as shown by its scanning electron microscopy images. Thermogravimetric analysis of PPMA-EGO indicates increased decomposition temperature of the PPMA matrix. Dynamic mechanical analysis showed enhanced storage modulus of PPMA-EGO. The maximum elastic modulus of PPMA-EGO was observed at 3 %wt of EGO. The electrical conductivity of PPMA-EGO was measured only for EGO concentrations above 2 %wt. The EGO concentration was found to be the most critical factor in the enhancement of the electrical conductivity of PPMA-EGO. Wide angle X-ray diffraction analysis of all polymer layered graphite oxide composites revealed no change in interlayer spacing of graphite layers, indicating the absence of EMAA intercalation in the graphite layers. The crystallisation temperature and crystallinity of all polymer layered graphite oxide composites were determined using differential scanning calorimetry. The results indicated that graphite oxide and expanded graphite oxides acted as nucleating agents in inducing the crystallisation of functionalised polyolefin in the layered composites. However, the degree of crystallinity of functionalised polyolefin decreased in the layered composites

Program and Abstracts of the Annual Meeting of the Georgia Academy of Science, 2011

The annual meeting of the Georgia Academy of Science took place March 23–24, 2011, at Gainesville State College, Oakwood, Georgia. Presentations were provided by members of the Academy who represented the following sections: I. Biological Sciences, II. Chemistry, III. Earth & Atmospheric Sciences, IV. Physics, Mathematics, Computer Science, Engineering & Technology, V. Biomedical Sciences, VI. Philosophy & History of Science, VII. Science Education, and VIII. Anthropology

Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Approaches for selective oxidation of methane to methanol

Methane activation chemistry, despite being widely reported in literature, remains to date a subject of debate. The challenges in this reaction are not limited to methane activation but extend to stabilization of the intermediate species. The low C-H dissociation energy of intermediates vs. reactants leads to CO2 formation. For selective oxidation, nature presents methane monooxygenase as a benchmark. This enzyme selectively consumes methane by breaking it down into methanol. To assemble an active site similar to monooxygenase, the literature reports Cu-ZSM-5, Fe-ZSM-5, and Cu-MOR, using zeolites and systems like CeO2/Cu2O/Cu. However, the trade-off between methane activation and methanol selectivity remains a challenge. Density functional theory (DFT) calculations and spectroscopic studies indicate catalyst reducibility, oxygen mobility, and water as co-feed as primary factors that can assist in enabling higher selectivity. The use of chemical looping can further improve selectivity. However, in all systems, improvements in productivity per cycle are required in order to meet the economical/industrial standards

Emerging electrocatalytic strategies for small molecule electrosynthesis

À la lumière du changement climatique et de l'épuisement des réserves de combustibles fossiles, l'innovation dans les technologies énergétiques vertes et durables devient un défi crucial. La fabrication de produits chimiques consomme de grandes quantités d'énergie et est responsable d'une part importante des émissions mondiales de carbone. Dans ce contexte, l'électrosynthèse, alimentée par de l'électricité renouvelable, peut remplacer de nombreux procédés thermochimiques industriels pour générer des carburants, des produits chimiques et des engrais. Plutôt que de nous concentrer sur des domaines qui ont reçu beaucoup d'attention ces dernières années (par exemple, l'électrolyse de l'eau et la réduction du CO2), nous avons exploré les domaines émergents de l'électrosynthèse hétérogène pour lesquels il existe un besoin substantiel. Dans le chapitre 3, nous soulignons l'importance de concevoir des électrocatalyseurs avec des sites actifs bien définis. Nous rapportons l'utilisation de la chimie réticulaire pour concevoir un système de modèle électrocatalytique à base d'organo-métallique conducteur avec des sites actifs moléculaires M-O4 pour l'oxydation électrochimique du 5-hydroxyméthylfurfural (HMFOR). L'activité des MOF portant des sites actifs Ni-O4 (Ni-CAT) et Co-O4 (Co-CAT) a été analysée avec des techniques spectroscopiques électrochimiques et operando pour élucider le mécanisme de réaction se produisant à la surface. Les expériences électrochimiques révèlent que le Co-CAT a un potentiel d'apparition plus précoce pour activer le HMFOR, par rapport à la plupart des catalyseurs établis, tandis que le Ni-CAT présente une cinétique plus rapide pour la conversion du 5-hydroxyméthylfurfural (HMF) en acide 2,5-furandicarboxylique (FDCA) . Nous avons déterminé que Ni-CAT atteignait des rendements de FDCA (notre molécule cible) de 98,7 %. L'efficacité faradique peut atteindre 86,8% d'efficacité faradique. La spectroscopie infrarouge indique le HMF avec un groupe aldéhyde lié à la surface comme intermédiaire clé dans le cycle catalytique, qui se forme une fois que l'oxydation M (II \ III) se produit. Ce travail illustre l'avantage d'utiliser des sites actifs moléculairement définis couplés à la spectroscopie operando pour fournir des informations fondamentales sur une variété de réactions électrosynthétiques et ouvrir la voie à la conception future de catalyseurs. Suite à ce projet, nous nous sommes tournés vers l'utilisation d'un réacteur à membrane sélective pour l'hydrogène afin d'explorer de nouveaux concepts de réaction et de catalyseurs. La clé ici était d'utiliser une feuille de Pd comme matériau qui réduisait les protons en *H dans un compartiment aqueux et transférait l'hydrogène dans un compartiment organique où il hydrogénait le réactif de choix. À l'aide d'un réacteur à membrane, nous avons pu séparer physiquement la réduction électrochimique de l'hydrogène et la chimie de l'hydrogénation d'une manière qui contournait l'utilisation du gaz H2 qui serait autrement nécessaire. Nous choisissons comme point de départ un produit chimique produit industriellement en excès, l'acétonitrile. Le réacteur à membrane Pd est appliqué pour hydrogéner complètement la liaison C≡N de l'acétonitrile. Avec succès, nous avons obtenu de l'ammoniac et de l'acétaldéhyde comme produits de réaction à un potentiel de début record de 0,4 V vs Ag/AgCl. Enfin, en concevant soigneusement une cellule spectroélectrochimique unique, nous avons pu effectuer des mesures spectroscopiques infrarouges pour visualiser le processus de réaction dans la membrane Pd et par conséquent proposé un mécanisme unique de réaction d'hydrolyse de l'imine (Chapitre 4). Dans le chapitre 5, nous choisissons d'innover dans un domaine émergent : la formation de liaisons électrochimiques C-N à partir de réactifs de petites molécules (par exemple CO2, NH3). Le mécanisme conventionnel de formation de liaisons électrochimiques C-N est basé sur le CO2RR électrochimique. Dans ce chapitre, nous proposons une stratégie orthogonale pour activer simultanément le CO2 et les N-réactifs en appliquant respectivement des impulsions de potentiel négatives et positives. Les nanoparticules de Cu sont utilisées comme catalyseur modèle, le CO2 agit comme réactif C et le NH3 agit comme réactif N pour le couplage C-N. Dans des conditions optimisées dans lesquelles la couverture *NH2 est maintenue à l'état stable tandis que Cu reste métallique, l'électrolyse pulsée augmente à la fois le taux de formation et la sélectivité des produits C-N urée, formamide et acétamide de 3 à 20 fois. En étendant le champ d'application à des réactifs C et N supplémentaires, ainsi qu'au couplage C-S, cette nouvelle approche démontre davantage sa valeur générale en électrosynthèse.In light of climate change and depleting fossil fuel reserves, innovating green and sustainable energy technologies becomes a critical challenge. Chemical manufacturing consumes large amounts of energy and is responsible for a substantial portion of global carbon emissions. Against this backdrop, electrosynthesis, powered by renewable electricity, can replace many industrial thermochemical processes to generate fuels, chemicals, and fertilizers. Rather than focusing on areas that have received much attention in recent years (e.g. water electrolysis and CO2 reduction), we explored emerging areas within heterogeneous electrosynthesis for which there is a substantial need. In chapter 3, we highlight the importance of designing electrocatalysts with well defined active sites. We report the use of reticular chemistry to design a conductive metal organic framework-based electrocatalytic model system with molecular M-O4 active sites for electrochemical oxidation of 5-hydroxymethylfurfural (HMFOR). The activity of MOFs bearing Ni-O4 (Ni-CAT) and Co-O4 (Co-CAT) active sites were analyzed with electrochemical and operando spectroscopic techniques to elucidate the reaction mechanism occurring on the surface. Electrochemical experiments reveal that Co-CAT has an earlier onset potential for enabling HMFOR, relative to most established catalysts, while the Ni-CAT shows faster kinetics for the conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). We determined that Ni-CAT achieved FDCA (our target molecule) yields of 98.7% yield. The faradic efficiency can reach out to 86.8% faradic efficiency. Infrared spectroscopy points to HMF with a surface-bound aldehyde group as the key intermediate in the catalytic cycle, which forms once the M(II\III) oxidation occurs. This work illustrates the advantage of utilizing molecularly defined active sites coupled with operando spectroscopy to provide fundamental insights into a variety of electrosynthetic reactions and pave the way for future catalyst design. Following this project, we turned to the use of a hydrogen-selective membrane reactor to explore more new reaction and catalysts concepts. The key here was using a Pd foil as a material that reduced protons to *H at an aqueous compartment and transferred the hydrogen through to an organic compartment where it hydrogenated the reactant of choice. Using a membrane reactor, we could physically separate electrochemical hydrogen reduction and hydrogenation chemistry in a manner that circumvented the use of H2 gas as would otherwise be necessary. We choose a chemical that is industrially produced in excess, acetonitrile, as a starting point. The Pd membrane reactor is applied to fully hydrogenate the C≡N bond of acetonitrile. Successfully, we obtained ammonia and acetaldehyde as reaction products at a record onset potential of 0.4 V vs Ag/AgCl. Finally, by carefully designing a unique spectroelectrochemical cell, we were able to carry out infrared spectroscopic measurements to visualize the reaction process in Pd-membrane and consequently proposed a unique imine-hydrolysis reaction mechanism (Chapter 4). In Chapter 5, we choose to innovate in an emerging area: electrochemical C-N bond formation from small molecule reactants (e.g. CO2, NH3). The conventional electrochemical C-N bond formation mechanism is based on electrochemical CO2RR. In this chapter, we propose an orthogonal strategy to simultaneously activate CO2 and N-reactants by applying negative and positive potential pulses, respectively. Cu nanoparticles are used as a model catalyst, CO2 acts as the C-reactant, and NH3 acts as the N-reactant for C-N coupling. Under optimized conditions in which *NH2 coverage is maintained at steady state while Cu remains metallic, pulsed electrolysis increases both the rate of formation and the selectivity of the C-N products urea, formamide and acetamide by 3-20 times. By extending the scope to additional C- and N-reactants, as well as C-S coupling, this new approach further demonstrates its general value in electrosynthesis

Isomeric olefinic periodic mesoporous organosilicas: an emerging class of versatile nanomaterials

Porous materials appear widely in nature and are the subject of intense study in many research areas owing to their unique properties. Their ability to interact with atoms, ions and molecules has lead to their wide spread applicability in sorption, catalysis, chromatography, ion exchange, micro-electronics, environmental technology, controlled drug release, . . . In the field of porous materials, scientists aim to control the size, shape, uniformity and periodicity of porous space and the atoms and molecules that define it. By controlling and fine-tuning these properties, materials can be engineered to meet the desired function and behaviour in a particular application. The presented research work describes the development, characterization and catalytic application of diastereoisomeric olefinic periodic mesoporous organosilicas (PMOs). PMOs are very unique in their compositional structure. The organic groups are covalently bonded within the siliceous network and hence are an intrinsic constituent of the mesoporous framework. The high loading and uniform distribution of organic groups in the pore walls of these open porous structures is a distinctive feature which allows for the easy tailoring of the PMO properties. From this perspective olefinic PMOs are very appealing, as they offer plenty of opportunities for surface modification based on olefin chemistry. To date, only limited research has been done on these very promising type of organic-inorganic hybrid materials and their potential in various applications has not been explored yet. The main goal of this research work has been the development of a novel class of versatile olefinic PMOs, which consist of diastereoisomerically configured organic bridges in their pore walls. The aim was to investigate new synthesis strategies which enable the synthesis of highly stable hybrid materials with controllable chemical and physical properties. By means of a detailed analysis of the developed PMO materials, an effort has also been made to understand the complex mechanisms involved in the supramolecular self-assembly process of ethenylene-bridged PMOs. Furthermore, with the intent of expanding the scope of olefinic PMOs, both the synthesis of new materials and the application thereof in catalysis has been studied