Kinetically controlled homogenization and transformation of crystalline fiber networks in supramolecular materials

Supramolecular materials with three-dimensional fiber networks have applications in many fields. For these applications, a homogeneous fiber network is essential in order to get the desired performance of a material. However, such a fiber network is hard to obtain, particularly when the crystallization of fiber takes place nonisothermally. In this work, a copolymer is used to kinetically control the nucleation and fiber network formation of a small molecular gelling agent, N-lauroyl-L-glutamic acid di-nbutylamide (GP-1) in benzyl benzoate. The retarded nucleation and enhanced mismatch nucleation of the gelator by the additive leads to the conversion of a mixed fiber network into a homogeneous network consisting of spherulites only. The enhanced structural mismatch of the GP-1 during crystallization is quantitatively characterized using the rheological data. This effect also leads to the transformation of an interconnecting (single) fiber network of GP-1 into a multidomain fiber network in another solvent, isostearyl alcohol. The approach developed is significant to the production of supramolecular materials with homogeneous fiber networks and is convenient to switch a single fiber network to a multidomain network without adjusting the thermodynamic driving force.

Architecture of supramolecular soft functional materials: from understanding to micro-/nanoscale engineering

This article gives an overview of the current progress of a class of supramolecular soft materials consisting of fiber networks and the trapped liquid. After discussing the up-to-date knowledge on the types of fiber networks and the correlation to the rheological properties, the gelation mechanism turns out to be one of the key subjects for this review. In this concern, the following two aspects will be focused upon: the single fiber network formation and the multi-domain fiber network formation of this type of material. Concerning the fiber network formation, taking place via nucleation, and the nucleation-mediated growth and branching mechanism, the theoretical basis of crystallographic mismatch nucleation that governs fiber branching and formation of three-dimensional fiber networks is presented. In connection to the multi-domain fiber network formation, which is governed by the primary nucleation and the subsequent formation of single fiber networks from nucleation centers, the control of the primary nucleation rate will be considered. Based on the understanding on the the gelation mechanism, the engineering strategies of soft functional materials of this type will be systematically discussed. These include the control of the nucleation and branching-controlled fiber network formation in terms of tuning the thermodynamic driving force of the gelling system and introducing suitable additives, as well as introducing ultrasound. Finally, a summary and the outlook of future research on the basis of the nucleation-growth-controlled fiber network formation are given.

Chromate replacement in coatings for corrosion protection of aerospace aluminium alloys

Mixed rare earth organophosphates have been investigated as potential corrosion inhibitors for AA2024-T3 with the aim of replacing chromate-based technologies. Cerium diphenyl phosphate (Ce(dpp) 3) and mischmetal diphenyl phosphate (Mm(dpp) 3) were added to epoxy coatings applied to AA2024-T3 panels and they were effective in reducing the amount and rate of filiform corrosion in high humidity conditions. Ce(dpp) 3 was the most effective and characterisation of the coating formulations showed approximately a factor of 5 reduction in both the number of corrosion filaments initiated as well as the length of these. Mm(dpp) 3 appeared to reduce the corrosion growth rate by a factor of 2 although it was the more effective inhibitor in solution studies. Spectroscopic characterisation of the coatings indicated that the cerium based inhibitor may disrupt network formation in the epoxy thus resulting in a coating that absorbed more water and allowed greater solubilisation of the corrosion inhibiting compound.

Contágio no modelo de Allen e Gale com infraestrutura bancária endógena

Neste trabalho investigamos a formação de network considerando agentes cautelosos. O modelo consiste em duas regiões com (n/2) bancos em cada, onde a interligação entre eles ocorre através e depósitos interbancários. Cada banco está sujeito a corrida bancária, ou devido a um choque negativo de agentes impacientes, ou devido a contaminação da corrida de um banco pertencente a infraestrutura bancária. Os bancos podem tentar eliminar a possibilidade de contágio ao fazer um número alto de inter-ligações. Para isso, é necessário uma coordenação entre todos os bancos. Se um banco não se prevenir de um contágio, ele impõe a todos os outros a possibilidade de contágio no pior cenário. Há duas regiões bem definidas de equilíbrio de nash simétrico com network estável, uma na qual todos os bancos se previnem do cenário de contágio no pior cenário e a outra na qual nenhum banco se previne. Devido ao problema de coordenação, o equilíbrio com contágio no pior cenário pode ocorrer mesmo sendo pareto dominado pelo equilíbrio sem contágio. Sob certas condições, o equilíbrio com contágio ocorre com um network pareto eficiente. Neste caso o network eficiente é diferente do network mais resiliente ao contágio.

The consumer litigation industry: chasing dragon kings in lawyer-client networks

The community of lawyers and their clients form a scale-free bipartite network that develops naturally as the outcome of the recommendation process through which lawyers form their client base. This process is an example of preferential attachment where lawyers with more clients are more likely to be recommended to new clients. Consumer litigation is an important market for lawyers. In large consumer societies, there always a signi cant amount of consumption disputes that escalate to court. In this paper we analyze a dataset of thousands of lawsuits, reconstructing the lawyer-client network embedded in the data. Analyzing the degree distribution of this network we noticed that it follows that of a scale-free network built by preferential attachment, but for a few lawyers with much larger client base than could be expected by preferential attachment. Incidentally, most of these also gured on a list put together by the judiciary of Lawyers which openly advertised the bene ts of consumer litigation. According to the code of ethics of their profession, lawyers should not stimulate clients into litigation, but it is not strictly illegal. From a network formation point of view, this stimulation can be seen as a separate growth mechanism than preferential attachment alone. In this paper we nd that this composite growth can be detected by a simple statistical test, as simulations show that lawyers which use both mechanisms quickly become the \Dragon-Kings" of the distribution of the number of clients per lawyer.

A organização social e o acesso à cultura: o caso das bibliotecas parque do Estado do Rio de Janeiro

Esta dissertação procura analisar qual a contribuição das Organizações Sociais para o acesso a direitos culturais, a partir da experiência das Bibliotecas Parque do Estado do Rio de Janeiro, em especial a de Manguinhos e a da Rocinha. Ciente de que as formas de cooperação para a efetivação de direitos culturais são múltiplas e que precisam ser pensadas a partir da inter-relação de vários atores e aspectos, todas invariavelmente necessitam desaguar em molduras de gestão viabilizadoras do acesso à cultura. A pesquisa adota o método do estudo de caso, valendo-se de pesquisas bibliográfica, documental e de campo. Apresenta o cenário de construção dos direitos culturais, em larga expansão no Brasil, e destaca que, para materializá-los, torna-se necessário estudar, avaliar e adotar modelos organizacionais alternativos aos tradicionais que caracterizam a administração pública direta e indireta. Aborda o campo da gestão e dos direitos culturais no contexto das três principais reformas do aparelho do Estado Republicano, ocorridas nas décadas de 30, 60 e 90, com ênfase na última, que incorpora a teoria da Nova Gestão Pública, base desta dissertação. Focaliza a Organização Social como modelo opcional à gestão de instituições ou programas culturais, a partir da realidade existente, das motivações, das vantagens e das perspectivas e aduz uma narrativa acerca do processo de concepção da legislação do estado do Rio de Janeiro. Verifica como surgiram esses equipamentos culturais e como se deu a formação da rede de Bibliotecas Parque. Descreve o processo de implantação das Organizações Sociais de Cultura no estado e apresenta o gestor das bibliotecas e sua relação com a secretaria de Cultura. Conclui que há necessidade de aperfeiçoamento de mecanismos de gestão, a fim de que o modelo possa, de fato, oferecer contribuição para o acesso a direitos culturais.

Influence of root-surface conditioning with acid and chelating agents on clot stabilization

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Synthesis and Structural Studies of Er3+ Containing Lead Cadmium Fluoroborate Glasses and Glass-Ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural studies on TeO2-PbO glasses

Binary tellurite-based glasses in the TeO2-PbO system were prepared and its structure investigated by means of Raman Scattering and X-ray Absorption Spectroscopy. Both spectroscopies indicate strong modifications of the first coordination shell around tellurium atoms when the PbO content increases revealing for lead its glassy network modifier role. Also, Pb L-3-edge EXAFS measurements reveal this structural role played by lead atoms, but the presence of a medium range order contribution indicates that lead also participates to the glassy network formation. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Electrical percolation during gelation of lithium doped siloxane-poly(oxyethylene) hybrids

Gelation mechanisms of lithium-doped Siloxane-Poly(oxyethylene) (PEO) hybrids containing polymer of two different molecular weight (500 and 1900 g/mol) were investigated through the evolution of the electrical properties during the solgel transition. The results of electrical measurements, performed by in-situ complex impedance spectroscopy, were correlated with the coordination and the dynamical properties of the lithium ions during the process as shown by Li-7 NMR measurements. For both hybrids sols, a decrease of the conductivity is observed at the initial gelation stage, due to the existence of an inverted percolation process consisting of the progressive separation of solvent molecules containing conducting species in isolated islands during the solid network formation. An increase of conductivity occurs at more advanced stages of gelation and aging, attributed to the increasing connectivity between PEO chains promoted by the formation of crosslinks of siloxane particles at their extremities, favoring hopping motions of lithium ions along the chains.

Redes dinâmicas de sensores sem fio ZigBee para aplicações de monitoramento e controle

Pós-graduação em Engenharia Elétrica - FEB

RHEOLOGICAL EVALUATION OF THE STRUCTURE OF ICE CREAM MIXES VARYING FAT BASE

This paper discusses the influence of fat type in the structure of ice cream, during its production by means of rheo-optical analysis. Fat plays an important part in the ice cream structure formation. It's responsible for the air stabilization, flavor release, texture and melting properties. The objective of this study was to use a rheological method to predict the fat network formation in ice cream with three types of fats (hydrogenated, low trans and palm fat). The three formulations were produced using the same methodology and ratio of ingredients. Rheo-optical measurements were taken before and after the ageing process, and the maximum compression force, overrun and melting profile were calculated in the finished product. The rheological analysis showed a better response from the ageing process from the hydrogenated fat, followed by the low trans fat. The formulation with palm fat showed greater differences between the three, where through the rheological tests a weaker destabilization of the fat globule membrane by the emulsifier was suggested. The overrun, texture measurements and meltdown profile has shown the distinction on the structure formation by the hydrogenated fat from the other fats.

Ferroelektrische Netzwerksynthese und ihre Charakterisierung

Deutsch:Diese Arbeit beschäftigt sich zum einen mit der Synthese neuer, vernetzbarer, ferroelektrischer Verbindungen, welche eine höhere spontane Polarisation und damit ein besseres Schaltverhalten nach Vernetzung aufweisen sollten. Dazu wurde in bekannte Systemen die Halogene Fluor, Chlor und Brom erfolgreich eingebaut. Desweiteren konnten neue Untersuchungmethoden für ferroelektrische, flüssigkristalline Netzwerke erfolgreich angewendet und weiterentwickelt werden. Damit gelang es z. B. neue Erkenntnisse über die elastischen Eigenschaften von LC-Elastomeren zu gewinnen, wobei es erstmalig gelang, Seifenblasen aus LC-Polymeren herzustellen und durch UV-Bestrahlung zu vernetzen. Durch die Messung des Radius in Abhängigkeit des Druckes war es möglich festzustellen, daß sich das Verhalten des Polymers, welches zunächst oberflächenspannungskontrolliert war, nach UV-Bestrahlung, in ein elastisches Verhalten änderte. Aus der Radius vs. Druckbeziehung war es möglich, Daten über die elastischen Eigenschaften zu erhalten. Die Ballone zeigten dabei typische, gummielastische Eigenschaften. Ein Einfluß der Mesophase (d.h. SA oder SC-Phase) auf die Eigenschaften der Ballone konnte dabei nicht festgestellt werden. Für die beiden hier untersuchten Systeme des inter- und intralyer vernetzbaren System konnte festgestellt werden, daß ihr elastisches Verhalten sehr ähnlich ist, ganz im Gegensatz zu den früheren elektrooptischen Untersuchungen. D. h. beide Systeme zeigten nach der Vernetzung bis auf einen Faktor 2 das gleiche elastische Verhalten. Im Gegensatz zu nematischen Elastomeren, welche am Phasenübergang zum Teil große thermoelastische Änderungen zeigen, zeigten die hier untersuchten Elastomere keine Änderung der elastischen Eigenschaften beim Phasenübergang, was sich u.a. auf die relativ hohen Vernetzungsdichten zurückführen läßt. Weiterhin wurde die Elektrostriktion in ferroelektrischen flüssigkristallinen Elastomerenfilmen untersucht, welche zu einem neuen Weltrekord des elektrostriktiven Effektes führte. Es wurden Schichtdickenänderungen von 4% bei einem angelegten Feld von 1,5 kV gemessen. Röntgenstreuexperimente an gespincoateten, vernetzten Polymerfilmen haben überdies gezeigt, daß der gemessene Effekt voll und ganz auf den elektroklinen Effekt zurück zu führen ist. Zum Schluß wurde ein neuer Weg ausgearbeitet, um flüssigkristalline Netzwerke unter Einsatz von weniger präparativer Chemie zu erhalten. Dazu wurde die Möglichkeit der Netzwerkbildung mit organischen Gelbildnern untersucht. In diesem Zusammenhang ist es erstmalig gelungen, ferroelektrische Flüssigkristalle reversibel in dem einen oder anderen Zustand orientiert zu stabilisieren, wobei beliebig oft zwischen den stabilisierten Zuständen gewechselt werden konnte.

Synaptic connectivity in micropatterned networks of neuronal cells

The presented thesis describes the formation of functional neuronal networks on an underlying micropattern. Small circuits of interconnected neurons defined by the geometry of the patterned substrate could be observed and were utilised as a model system of reduced complexity for the behaviour of neuronal network formation and activity. The first set of experiments was conducted to investigate aspects of the substrate preparation. Micropatterned substrates were created by microcontact printing of physiological proteins onto polystyrene culture dishes. The substrates displayed a high contrast between the repellant background and the cell attracting pattern, such that neurons seeded onto these surfaces aligned with the stamped structure. Both the patterning process and the cell culture were optimised, yielding highly compliant low-density networks of living neuronal cells. In the second step, cellular physiology of the cells grown on these substrates was investigated by patch-clamp measurements and compared to cells cultivated under control conditions. It could be shown that the growth on a patterned substrate did not result in an impairment of cellular integrity nor that it had an impact on synapse formation or synaptic efficacy. Due to the extremely low-density cell culture that was applied, cellular connectivity through chemical synapses could be observed at the single cell level. Having established that single cells were not negatively affected by the growth on patterned substrates, aspects of network formation were investigated. The formation of physical contact between two cells was analysed through microinjection studies and related to the rate at which functional synaptic contacts formed between two neighbouring cells. Surprisingly, the rate of synapse formation between physically contacting cells was shown to be unaltered in spite of the drastic reduction of potential interaction partners on the micropattern. Additional features of network formation were investigated and found consistent with results reported by other groups: A different rate of synapse formation by excitatory and inhibitory neurons could be reproduced as well as a different rate of frequency-dependent depression at excitatory and inhibitory synapses. Furthermore, regarding simple feedback loops, a significant enrichment of reciprocal connectivity between mixed pairs of excitatory and inhibitory neurons relative to uniform pairs could be demonstrated. This phenomenon has also been described by others in unpatterned cultures [Muller, 1997] and may therefore be a feature underlying neuronal network formation in general. Based on these findings, it can be assumed that inherent features of neuronal behaviour and cellular recognition mechanisms were found in the cultured networks and appear to be undisturbed by patterned growth. At the same time, it was possible to reduce the complexity of the forming networks dramatically in a cell culture on a patterned surface. Thus, features of network architecture and synaptic connectivity could be investigated on the single cell level under highly defined conditions.

Entstehung und Dynamik des Keratinfilament-Netzwerks

Das zytoplasmatische Zytoskelett besteht aus drei Filamentsystemen, die aus Aktin, Tubulin und Intermediärfilamentproteinen aufgebaut sind und dreidimensionale Netzwerke ausbilden. Das Intermediärfilamentsystem, dem vor allem mechanische Stabilisierungsfunktionen zugesprochen werden, unterscheidet sich von den anderen durch seine Fähigkeit, spontan aus seinen Polypeptiduntereinheiten ohne weitere Kofaktoren zu polymerisieren und durch seinen unpolaren Aufbau. Es ist bis heute unbekannt, wie Intermediärfilamentnetzwerke in vivo moduliert werden und wie ihre Anordnung in den Kontext des Gesamtzytoskeletts koordiniert wird. Am Beispiel der epithelialen Intermediärfilamentproteine, den Keratinen, sollte daher untersucht werden, wie und wo neue Intermediärfilamente entstehen, welche Bedeutung den anderen Filamentsystemen bei dem Netzwerkaufbau und –Turn-Over zukommen und wie die Netzwerkbildung gesteuert wird. Zur Beantwortung dieser Fragestellungen wurden Zellklone hergestellt, die fluoreszierende Keratine synthetisieren. In der Zelllinie SK8/18-2, deren gesamtes Netzwerk aus derartigen Chimären aufgebaut ist, konnten anhand von mikroskopischen Zeitrafferaufnahmen der Fluoreszenzmuster Keratinfilamentvorläufer (KFP) identifiziert und deren Dynamik direkt in lebenden Zellen verfolgt werden. Es konnte gezeigt werden, dass die KFP in einem Plasmamembran-nahen Bereich entstehen, in dem sie zuerst als punktförmige Partikel detektiert werden. Nach einer initialen, sphäroidalen Wachstumsphase elongieren die Partikel zu kleinen Filamentstückchen. Diese können miteinander fusionieren und werden über ihre Enden in das periphere Netzwerk integriert. Der Wachstumsprozess ist gekoppelt an eine kontinuierliche, langsame Bewegung in Richtung auf das Zellzentrum. Diese Motilität sistiert vollständig nach pharmakologisch induziertem Abbau der Aktinfilamente. In Zeitraffer-aufnahmen kann jedoch in derartig behandelten Zellen ein wesentlich schnellerer Transport, der in verschiedene Richtungen verläuft und durch lange Ruhephasen unterbrochen wird, beobachtet werden. Dieser Modus, der gelegentlich auch in unbehandelten Zellen gefunden wurde, ist abhängig von intakten Mikrotubuli. Erst durch Zerstörung der Aktinfilamente und der Mikrotubuli erlischt die Motilität der KFPs vollständig. Bei der Suche nach Regulatoren der Keratinnetzwerkbildung wurde die p38 MAPK als zentraler Faktor identifiziert. Erstmals konnte eine direkte räumliche und zeitliche Korrelation zwischen einer spezifischen Enzymaktivität durch Nachweis der phosphorylierten p38 MAPK, der daraus folgenden Phosphorylierung eines Keratins, hier Serin 73 des Keratin 8, und der daraus resultierenden Veränderung des Netzwerkaufbaus, d. h. der Ausbildung von Keratingranula, nachgewiesen werden. Diese koordinierten Veränderungen wurden in unterschiedlichen Stresssituationen in verschiedenen Zellsystemen und in Zellen mit mutierten Keratinen beobachtet. Genetische (shRNA) und pharmakologische Manipulationen der p38 MAPK-Aktivität deuten auf einen engen kausalen Zusammenhang hin.