Relevant bibliographies by topics / Preformed fibrils

Academic literature on the topic 'Preformed fibrils'

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Published: 10 December 2022
Last updated: 28 January 2023

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Journal articles on the topic "Preformed fibrils"

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Ogawa, Kenjirou, Ayumi Ishii, Aimi Shindo, Kunihiro Hongo, Tomohiro Mizobata, Tetsuya Sogon, and Yasushi Kawata. "Spearmint Extract Containing Rosmarinic Acid Suppresses Amyloid Fibril Formation of Proteins Associated with Dementia." Nutrients 12, no. 11 (November 13, 2020): 3480. http://dx.doi.org/10.3390/nu12113480.

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Neurological dementias such as Alzheimer’s disease and Lewy body dementia are thought to be caused in part by the formation and deposition of characteristic insoluble fibrils of polypeptides such as amyloid beta (Aβ), Tau, and/or α-synuclein (αSyn). In this context, it is critical to suppress and remove such aggregates in order to prevent and/or delay the progression of dementia in these ailments. In this report, we investigated the effects of spearmint extract (SME) and rosmarinic acid (RA; the major component of SME) on the amyloid fibril formation reactions of αSyn, Aβ, and Tau proteins in vitro. SME or RA was added to soluble samples of each protein and the formation of fibrils was monitored by thioflavin T (ThioT) binding assays and transmission electron microscopy (TEM). We also evaluated whether preformed amyloid fibrils could be dissolved by the addition of RA. Our results reveal for the first time that SME and RA both suppress amyloid fibril formation, and that RA could disassemble preformed fibrils of αSyn, Aβ, and Tau into non-toxic species. Our results suggest that SME and RA may potentially suppress amyloid fibrils implicated in the progression of Alzheimer’s disease and Lewy body dementia in vivo, as well.
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Karunarathne, Kanchana, Nabila Bushra, Olivia Williams, Imad Raza, Laura Tirado, Diane Fakhre, Fadia Fakhre, and Martin Muschol. "Self-Assembly of Amyloid Fibrils Into 3D Gel Clusters Versus 2D Sheets." Biomolecules 13, no. 2 (January 24, 2023): 230. http://dx.doi.org/10.3390/biom13020230.

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The deposition of dense fibril plaques represents the pathological hallmark for a multitude of human disorders, including many neurodegenerative diseases. Fibril plaques are predominately composed of amyloid fibrils, characterized by their underlying cross beta-sheet architecture. Research into the mechanisms of amyloid formation has mostly focused on characterizing and modeling the growth of individual fibrils and associated oligomers from their monomeric precursors. Much less is known about the mechanisms causing individual fibrils to assemble into ordered fibrillar suprastructures. Elucidating the mechanisms regulating this “secondary” self-assembly into distinct suprastructures is important for understanding how individual protein fibrils form the prominent macroscopic plaques observed in disease. Whether and how amyloid fibrils assemble into either 2D or 3D supramolecular structures also relates to ongoing efforts on using amyloid fibrils as substrates or scaffolds for self-assembling functional biomaterials. Here, we investigated the conditions under which preformed amyloid fibrils of a lysozyme assemble into larger superstructures as a function of charge screening or pH. Fibrils either assembled into three-dimensional gel clusters or two-dimensional fibril sheets. The latter displayed optical birefringence, diagnostic of amyloid plaques. We presume that pH and salt modulate fibril charge repulsion, which allows anisotropic fibril–fibril attraction to emerge and drive the transition from 3D to 2D fibril self-assembly.
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Ferreira, Elisabete, Zaida L. Almeida, Pedro F. Cruz, Marta Silva e Sousa, Paula Veríssimo, and Rui M. M. Brito. "Searching for the Best Transthyretin Aggregation Protocol to Study Amyloid Fibril Disruption." International Journal of Molecular Sciences 23, no. 1 (December 30, 2021): 391. http://dx.doi.org/10.3390/ijms23010391.

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Several degenerative amyloid diseases, with no fully effective treatment, affect millions of people worldwide. These pathologies—amyloidoses—are known to be associated with the formation of ordered protein aggregates and highly stable and insoluble amyloid fibrils, which are deposited in multiple tissues and organs. The disruption of preformed amyloid aggregates and fibrils is one possible therapeutic strategy against amyloidosis; however, only a few compounds have been identified as possible fibril disruptors in vivo to date. To properly identify chemical compounds as potential fibril disruptors, a reliable, fast, and economic screening protocol must be developed. For this purpose, three amyloid fibril formation protocols using transthyretin (TTR), a plasma protein involved in several amyloidoses, were studied using thioflavin-T fluorescence assays, circular dichroism (CD), turbidity, dynamic light scattering (DLS), and transmission electron microscopy (TEM), in order to characterize and select the most appropriate fibril formation protocol. Saturation transfer difference nuclear magnetic resonance spectroscopy (STD NMR) was successfully used to study the interaction of doxycycline, a known amyloid fibril disruptor, with preformed wild-type TTR (TTRwt) aggregates and fibrils. DLS and TEM were also used to characterize the effect of doxycycline on TTRwt amyloid species disaggregation. A comparison of the TTR amyloid morphology formed in different experimental conditions is also presented.
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Musteikyte, Greta, Mantas Ziaunys, and Vytautas Smirnovas. "Methylene blue inhibits nucleation and elongation of SOD1 amyloid fibrils." PeerJ 8 (August 14, 2020): e9719. http://dx.doi.org/10.7717/peerj.9719.

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Protein aggregation into highly-structured amyloid fibrils is linked to several neurodegenerative diseases. Such fibril formation by superoxide dismutase I (SOD1) is considered to be related to amyotrophic lateral sclerosis, a late-onset and fatal disorder. Despite much effort and the discovery of numerous anti-amyloid compounds, no effective cure or treatment is currently available. Methylene blue (MB), a phenothiazine dye, has been shown to modulate the aggregation of multiple amyloidogenic proteins. In this work we show its ability to inhibit both the spontaneous amyloid aggregation of SOD1 as well as elongation of preformed fibrils.
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Yang, Yaqi, Shiwu Li, Qin Zhang, Ying Kuang, Anjun Qin, Meng Gao, Feng Li, and Ben Zhong Tang. "An AIE-active theranostic probe for light-up detection of Aβ aggregates and protection of neuronal cells." Journal of Materials Chemistry B 7, no. 15 (2019): 2434–41. http://dx.doi.org/10.1039/c9tb00121b.

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An AIE-active probe of Cur-N-BF2 is developed for light-up detection of Aβ fibrils and plaques, inhibition of Aβ fibrillation, disassembly of preformed Aβ fibrils, and protection of neuronal cells.
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Tabassum, Shatera, Abdullah Md Sheikh, Shozo Yano, Takahisa Ikeue, Shingo Mitaki, Makoto Michikawa, and Atsushi Nagai. "A Cationic Gallium Phthalocyanine Inhibits Amyloid β Peptide Fibril Formation." Current Alzheimer Research 17, no. 7 (November 16, 2020): 589–600. http://dx.doi.org/10.2174/1567205017666201008112002.

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Background: Amyloid β (Aβ) peptide deposition is considered as the main cause of Alzheimer’s disease (AD). Previously, we have shown that a Zn containing neutral phthalocyanine (Zn-Pc) inhibits Aβ fibril formation. Objective: The objective of this study is to investigate the effects of a cationic gallium containing Pc (GaCl-Pc) on Aβ fibril formation process. Methods and Results: Aβ fibril formation was induced by incubating synthetic Aβ peptides in a fibril forming buffer, and the amount of fibril was evaluated by ThT fluorescence assay. GaCl-Pc dosedependently inhibited both Aβ1-40 and Aβ1-42 fibril formation. It mainly inhibited the elongation phase of Aβ1-42 fibril formation kinetics, but not the lag phase. Western blotting results showed that it did not inhibit its oligomerization process, rather increased it. Additionally, GaCl-Pc destabilized preformed Aβ1- 42 fibrils dose-dependently in vitro condition, and decreased Aβ levels in the brain slice culture of APP transgenic AD model mice (J20 strain). Near-infrared scanning results showed that GaCl-Pc had the ability to bind to Aβ1-42. MTT assay demonstrated that GaCl-Pc did not have toxicity towards a neuronal cell line (A1) in culture rather, showed protective effects on Aβ-induced toxicity. Moreover, it dosedependently decreased Aβ-induced reactive oxygen species levels in A1 culture. Conclusion: Thus, our result demonstrated that GaCl-Pc decreased Aβ aggregation and destabilized the preformed fibrils. Since cationic molecules show a better ability to cross the blood-brain barrier, cationic GaCl-Pc could be important for the therapy of AD.
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Almeida, Zaida L., and Rui M. M. Brito. "Amyloid Disassembly: What Can We Learn from Chaperones?" Biomedicines 10, no. 12 (December 17, 2022): 3276. http://dx.doi.org/10.3390/biomedicines10123276.

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Protein aggregation and subsequent accumulation of insoluble amyloid fibrils with cross-β structure is an intrinsic characteristic of amyloid diseases, i.e., amyloidoses. Amyloid formation involves a series of on-pathway and off-pathway protein aggregation events, leading to mature insoluble fibrils that eventually accumulate in multiple tissues. In this cascade of events, soluble oligomeric species are formed, which are among the most cytotoxic molecular entities along the amyloid cascade. The direct or indirect action of these amyloid soluble oligomers and amyloid protofibrils and fibrils in several tissues and organs lead to cell death in some cases and organ disfunction in general. There are dozens of different proteins and peptides causing multiple amyloid pathologies, chief among them Alzheimer’s, Parkinson’s, Huntington’s, and several other neurodegenerative diseases. Amyloid fibril disassembly is among the disease-modifying therapeutic strategies being pursued to overcome amyloid pathologies. The clearance of preformed amyloids and consequently the arresting of the progression of organ deterioration may increase patient survival and quality of life. In this review, we compiled from the literature many examples of chemical and biochemical agents able to disaggregate preformed amyloids, which have been classified as molecular chaperones, chemical chaperones, and pharmacological chaperones. We focused on their mode of action, chemical structure, interactions with the fibrillar structures, morphology and toxicity of the disaggregation products, and the potential use of disaggregation agents as a treatment option in amyloidosis.
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Paul, Ashim, Wen-Hao Li, Guru KrishnaKumar Viswanathan, Elad Arad, Satabdee Mohapatra, Gao Li, Raz Jelinek, Ehud Gazit, Yan-Mei Li, and Daniel Segal. "Tryptophan–glucosamine conjugates modulate tau-derived PHF6 aggregation at low concentrations." Chemical Communications 55, no. 97 (2019): 14621–24. http://dx.doi.org/10.1039/c9cc06868f.

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Jha, Anjali, Vandana Ghormade, Henry Kolge, and Kishore M. Paknikar. "Dual effect of chitosan-based nanoparticles on the inhibition of β-amyloid peptide aggregation and disintegration of the preformed fibrils." Journal of Materials Chemistry B 7, no. 21 (2019): 3362–73. http://dx.doi.org/10.1039/c9tb00162j.

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Maity, Debabrata, Sunil Kumar, Ruyof AlHussein, Lothar Gremer, Madeline Howarth, Laura Karpauskaite, Wolfgang Hoyer, Mazin Magzoub, and Andrew D. Hamilton. "Sub-stoichiometric inhibition of IAPP aggregation: a peptidomimetic approach to anti-amyloid agents." RSC Chemical Biology 1, no. 4 (2020): 225–32. http://dx.doi.org/10.1039/d0cb00086h.

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Naphthalimide-appended oligopyridylamide peptidomimetic modulate islet amyloid polypeptide amyloidogenesis and disaggregate preformed oligomers and fibrils into non-toxic conformations at substoichiometric concentration.
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Dissertations / Theses on the topic "Preformed fibrils"

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Crankshaw, Mark Ian. "Fabrication and properties of fibrous preforms." Thesis, University of Cambridge, 2000. https://www.repository.cam.ac.uk/handle/1810/251698.

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Jackson, Christopher Bryan. "Liquid metal infiltration of fibrous ceramic preforms." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393792.

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Masur, Lawrence Jay 1956. "Infiltration of fibrous preforms by a pure metal." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14698.

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Shields, Karen M. "Resin transfer molding with powder-coated preforms." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/17988.

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Saadi, Mohamed. "Etude et realisation d'un four pour l'etirage des preformes de fibres optiques en polymere." Toulouse 3, 1987. http://www.theses.fr/1987TOU30295.

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Dans ce memoire, l'auteur donne un rappel des principales caracteristiques des fibres optiques et des differentes causes de l'attenuation dans les fibres optiques en polymere. Les pertes de lumiere induites lors de l'etape d'etirage sont importantes; pour les reduire il faut assurer une repartition homogene de la temperature sur le diametre de la preforme en polymere. Cette etude traite la realisation d'un systeme de chauffage permettant de remplir une telle condition. L'auteur evoque les differents modes de transfert thermique: convection, conduction rayonnement. Compte tenu de la mauvaise conductivite thermique des polymeres et de leurs spectres d'absorption, le choix s'est porte sur un chauffage par rayonnement a l'aide de lampes a incandescence. Un premier prototype du four a ete construit. Pour evaluer ses performances, l'auteur determine la repartition de l'energie lumineuse dans le four et le profil de temperature a l'interieur de la preforme. Ces resultats experimentaux sont confirmes par les calculs theoriques, notamment par la resolution de l'equation de la chaleur, ainsi les courbes theoriques sont comparees aux courbes experimentales a partir des mesures sur la preforme. Enfin, les resultats de cette etude ont permis de proposer les ameliorations a apporter a ce premier prototype du four. Le four sous sa forme definitive est maintenant operationnel, il est installe sur la tout a fibrer. Des essais realises dans des conditions proches de l'etirage reel, c'est-a-dire sur une preforme en mouvement montrent que ce dernier prototype assure une bonne homogeneite de la temperature dans la preforme
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Gusken, Edmilton. "Dopagem de erbio em preforma de silica nanoestruturada para fibras opticas." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264870.

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Orientador: Carlos Kenichi Suzuki
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: A emissão do érbio na região de comprimentos de onda usada em comunicações ópticas tem despertado grande interesse tecnológico, especialmente quando este é incorporado à matriz de sílica. Entretanto, a dificuldade maior está na sua inserção em concentrações elevadas e de forma homogênea, e mesmo na atualidade, o mecanismo de dopagem da sílica com érbio ainda não é totalmente conhecido. Nesta pesquisa, foi desenvolvido um esforço concentrado no trabalho de entender e controlar a nanoporosidade da sílica através de diversos parâmetros de fabricação usando a técnica de deposição axial fase vapor, e também por tratamento térmico posterior à deposição. Duas metodologias de dopagem do érbio foram utilizadas: (i) imersão da preforma de sílica nanoestruturada em solução de c1oretode érbio em etanol; e (ii) deposição simultânea da solução de érbio aspergido com nanopartículas de sílica sintetizados em chama de Hz/Oz. A utilização da primeira metodologia de dopagem, juntamente com os resultados de estudo de caracterização, tiveram como principal mérito o entendimento do mecanismo de incorporação do érbio em nível nanoestrutural. A segunda metodologia demonstrou a alta eficiência e economia do método com a incorporação de alguns milhares de ppm's atômico de érbio com a correspondente resposta fotoluminescente
Abstract: A special property of erbium to emit light in the wavelength used for optical communications has aroused great technological interest, particularly for erbium doped fiber and devices. However, the key point of this technology is to get high concentration and homogeneouserbium doping into silica structure. Even now, the doping mechanism of erbium in silica glass is still not well known. A research work to study and to control the nanoporosity in silica glass has presently been developed by using various processing parameters of vapor phase axial deposition technique. Post-deposition heat treatment to control the distribution of nanoporosity has also been applied. Two methods to dope erbium have been developed: (i) immersion of nanostructured silica preform into a solution of erbium chloride and ethanol, and (ii) simultaneousdeposition of silica nanopartic1es and vaporized erbium chloride in Hz/Oz flame. The merit of the first doping methodology was to understand the doping mechanism in nanostructurallevel. And the result of the second technique demonstrated a new procedure to obtain highIy efficient and low cost erbium doped silica preform containing a concentration of few thousands atomic ppm with corresponding photoluminescence response
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
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Butts, Mark D. "Nondestructive examination of nicalon fiber composite preforms using x-ray tomographic microscopy." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19959.

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Sharif, Tahir. "Robotic approach to low-cost manufacturing of 3D preforms with dry fibres." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/robotic-approach-to-lowcost-manufacturing-of-3d-preforms-with-dry-fibres(d25f48b9-0d9e-4d78-a2dd-e00da1d127c7).html.

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High-performance fibres such as carbon, glass and kevlar are very promising for aerospace applications because of their high strength, stiffness, impact damage and excellent fatigue life. The high cost of the prepreg materials such as pre-impregnated fibre tape/tow and fabrics, and limitations of existing manufacturing processes are a big challenge for the aerospace industry to meet increasing performance demands. Their benefits can only be achieved by using low cost materials and manufacturing methods. In the past three or four decades, there have been substantial technological developments, which are governed by the new materials and their associated manufacturing techniques. The production of carbon fibre is slow and capital intensive, therefore, carbon manufactures produce higher tow counts (number of filaments) to increase production through-put in order to reduce its cost. In other words, 12k carbon tow is much cheaper than 6k or 3k carbon tow. In many applications finer tows are desirable. In this thesis, a fully automated laser feedback tow splitting line has been developed to split higher tow counts (12k spool) into smaller tow counts (split into 6k spools) in order to produce low cost material. The quality of the split tows has been evaluated by recording the data online during the splitting process. The recorded data was later analysed by statistical tools. A four axis modular gantry robotic system has been developed at the University of Manchester in order to deposit dry fibres in a completely flexible manner. To facilitate robotic preforming, an end-effector and mould have been designed and developed in this research. The tow placement program was written in the CoDeSys software which is then uploaded into the motion controller to perform specific motions. The cross-ply laminates have been manufactured by the proposed robotic system using split 6k (produced by the tow splitting process) and original 12k carbon tows. Mechanical test of both composites (12k and split 6k) are presented. A tufting process has been developed and conducted by the robotic system in order to manufacture 3D preforms. The tufted composite was compared with 3D woven and stitched 2D broadcloth in terms of the tensile and interlaminar shear strength properties. X-ray tomography has been conducted to investigate preform geometrical variations of manufactured composites. In addition, preforming cost models have been developed for robotic fibre placement and 3D weaving.
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Wong, Terence. "A new technique for measuring the wettability of fibrous preforms by liquid metal." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14596.

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Dini, Danilo Cesar. "Medida de birrefringencia e sua diminuição por rotação de preforma em fibras opticas monomodo." [s.n.], 1988. http://repositorio.unicamp.br/jspui/handle/REPOSIP/261384.

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Orientador : Evandro Conforti
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica
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Resumo: Apresentam-se os resultados obtidos na caracterização comprimento de batimento e, portanto, da Birrefringência Modal em fibras ópticas monomodo de alta birrefringência. O trabalho discute as montagens ópticas necessárias para a realização das medidas do comprimento de batimento utilizando-se três métodos: método do espalhamento Rayleigh, método da varredura em frequência e método do corte. Além disso, medidas do grau de polarização na saída da fibra foram realizadas. Apresentam-se, também, os resultados dos retardos medidos em fibras ópticas monomodo de baixa birrefringência, obtidas por rotação da preforma. Essas fibras foram desenvolvidas especialmente para este trabalho, tendo sido comparadas com fibras da mesma preforma obtidas com puxamento feito sem a rotação da preforma. o sistema de rotação da preforma, desenvolvido para o puxamento das fibras ópticas, e também descrito. A influência deste processo de fabricação nas propriedades das fibras obtidas foi avaliado através das medidas de geometria e de atenuação espectral. Finalmente, a partir da utilização do modelo teórico de Barlow et al.,mostra-se o efeito da rotação da preforma no retardo apresentado por essas fibras
Abstract: The results obtained in the characterization of the beat length and, therefore, of the Modal Birefringence in high- birefringence single-mode optical fibers are presented. The work discusses the optical mountings used for making the measurements of the beat length using three methods: Rayleigh scattering method, the frequency-sweeping method and the cut-back method. Besides this, measurements of the degree of polarization at the fiber output were made. AIso the results of measurement of retardation in Iow-birefringence single-mode optical fibers, obtained by spinning the preform are presented. Such fibers were developed specially for this work, and the results were compared with fibers obtained from the same preform by a drawing process without spinning the preform. The apparatus developed for spinning the preform during the drawing process of the optical fiber is also described. The influence of this fabrication process on the properties of the fibers obtained was evaluated by geometrical and spectral atenuation measurements. Finally, using the theoretical model of Barlow et aI., we show the effect of the preform spinning on the retardation presented by these fibers
Mestrado
Mestre em Ciências
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Books on the topic "Preformed fibrils"

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Progress report 1, for the period 01/01/93 to 06/30/93 for the project titled graphite fiber textile preform/copper matrix composites. [Washington, DC: National Aeronautics and Space Administration, 1993.

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Book chapters on the topic "Preformed fibrils"

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Zhang, Bin, Victoria Kehm, Ron Gathagan, Susan N. Leight, John Q. Trojanowski, Virginia M. Y. Lee, and Kelvin C. Luk. "Stereotaxic Targeting of Alpha-Synuclein Pathology in Mouse Brain Using Preformed Fibrils." In Methods in Molecular Biology, 45–57. New York, NY: Springer New York, 2019. http://dx.doi.org/10.1007/978-1-4939-9124-2_5.

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Worsley, Marcus A., James P. Lewicki, and Theodore F. Baumann. "Carbon Nanotube-Based Aerogels as Preformed Porous Fibrous Network for Reinforcing Lightweight Composites." In Porous lightweight composites reinforced with fibrous structures, 245–66. Berlin, Heidelberg: Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-53804-3_10.

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Kainer, K. U., H. Dieringa, P. Schulz, and J. Reiter. "Formation of Mg2Si by Infiltration of C-Fibres-Si-Hybrid-Preforms." In Magnesium Alloys and their Applications, 240–45. Weinheim, FRG: Wiley-VCH Verlag GmbH & Co. KGaA, 2006. http://dx.doi.org/10.1002/3527607552.ch37.

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Eberling-Fux, N., R. Pailler, A. Guette, Sebastien Bertrand, and Eric Philippe. "Impregnation of 3D Woven Carbon Fibre Preforms by Electrophoretic Deposition of Single and Mix of Non Oxide Ceramic Nanoscale Powders, and Densification of the Composite Material." In Advanced Inorganic Fibrous Composites V, 91–96. Stafa: Trans Tech Publications Ltd., 2006. http://dx.doi.org/10.4028/3-908158-06-0.91.

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PELLETIER, S. E., J. MASSOL, and Y. BIENVENU. "ON THE SOLIDIFICATION PROCESSING OF ALUMINIUM BASED FILAMENTARY PREFORMS REINFORCED BY CARBON FIBRES." In Interfacial Phenomena in Composite Materials '91, 290–92. Elsevier, 1991. http://dx.doi.org/10.1016/b978-0-7506-0356-0.50084-8.

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Patel, Sangdil I., and Fred J. Davis. "Liquid crystalline polymers." In Polymer Chemistry. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198503095.003.0014.

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The idea of combining the anisotropic behaviour of liquid crystalline materials with the properties of macromolecular systems was first suggested by Onsanger and subsequently Flory. The actual realization that such systems could exist came from studies of natural polymers such as the tobacco mosaic virus. Interest in these systems intensified with the development of highstrength systems, based on rigid-rod systems, notably the aramid fibres, however, liquid crystallinity in such systems occurs only at high temperatures, usually close to the decomposition point of the polymer. It was only in the late 1970s that the design criteria for liquid crystalline polymers became apparent, the secret being largely in the decoupling of the rigid aromatic groups which give rise to the anisotropic behaviour. As a result of these ideas two classifications of liquid crystalline materials were described. Main-chain liquid crystalline polymers, are those in which rigid aromatic molecules form part of the polymer backbone, either as a continuous chain or separated by a series of methylene groups in order to lower temperature at which liquid crystalline phase behaviour is observed. Side-chain systems resemble the comb-like systems studied by Shibaev and Plate, and have the rigid aromatic groups attached as a side-chain. In general, the monomer systems required for main-chain liquid crystalline polymers are relatively simple; synthetically these systems are prepared by step-growth methods and the main challenge is often maintaining sufficient solubility to allow suitable chain-lengths to be grown (an example of how such problems might be overcome is given in Chapter 4). Side-chain systems tend to be produced from more complex structural sub-units, and may be produced either by polymerization of the appropriate monomer or by functionalization of a preformed polymer backbone. Examples of both approaches are given in this chapter. From a practical viewpoint, the advantage of side-chain systems is that they tend to be much more soluble in common organic solvents and also that thermal phase transitions occur at reasonable temperatures (reasonable being well below the temperature at which the polymer decomposes). A further advantage of such side-chain systems is that the phase behaviour can be effectively tuned through the chemical modifications of the three components, namely the side-group, the flexible coupling chain and the polymer backbone.
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Conference papers on the topic "Preformed fibrils"

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Erdal, Merve, and Selçuk Güçeri. "Preform-Particle-Flow Interactions in Impregnation of Fibrous Preforms With Particle-Filled Resin." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0464.

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Abstract Particle-filled preceramic polymer injection into woven fiber preforms is currently under investigation as a means of processing dense, complex-shaped ceramic composites. The distribution of filler particles as a result of filtration during their impregnation into dense fiber preforms, has a crucial effect on the properties of the end product. In general, highly filtered particle distributions are not desirable since they lead to nonhomogeneous part microstructure and hence, mechanical properties of the composite. In order to understand how various process parameters (injection velocity, inlet particle concentration, fiber preform permeability, etc.) interact during impregnation and to ultimately control the amount of filtration, a process model is presented. A multi-dimensional, transient particle filtration formulation is coupled with isothermal, anisotropic Darcy’s flow to predict filler concentration profiles during molding of complex shapes. The permeability of the preform, porosity of the flow domain, viscosity of the impregnating resin and filtration coefficient are all affected by the particle deposition and they constitute the nonlinearity in the coupled flow and filtration equations. Results for 2-D impregnation into complex preforms are presented and methods for manipulating particle distribution are discussed.
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Jasim, Ali A., Ondrej Podrazký, Pavel Peterka, Michal Kamrádek, Filip Todorov, and Pavel Honzátko. "Reduction of water penetration into optical fiber preforms for improving preform shaping based on CO2 laser (Conference Presentation)." In Micro-Structured and Specialty Optical Fibres VI, edited by Christian-Alexander Bunge, Kyriacos Kalli, and Pavel Peterka. SPIE, 2020. http://dx.doi.org/10.1117/12.2555882.

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3

Kowalik, Waldemar, and Marian Michalski. "Interferometer For Testing Waveguide Preforms." In Optical Fibres and Their Applications, edited by Ryszard S. Romaniuk and Mieczyslaw Szustakowski. SPIE, 1986. http://dx.doi.org/10.1117/12.938969.

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4

Liang, Zhiyong, Chuck Zhang, Ben Wang, and Chiang Shih. "In-Situ Measurement and Monitoring of Fiber Preform Permeability for Liquid Composite Molding." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1796.

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Abstract In a liquid composite molding (LCM) process such as resin transfer molding (RTM), quality control depends on an in-situ permeability profile of the fibrous preform taken just before resin injection. However, the conventional permeability measurement method, which uses liquid (oil or resin) as its working fluid, only measures the average preform permeability in an off-line mode. It cannot be used to create an in-situ permeability profile because of fiber pollution, and cannot be used to reveal local permeability variations of preform. This study develops a new permeability characterization method that uses gas flow and pressure profiles to measure preform permeability variation in a closed mold assembly. This method is based upon two research findings: (1) that the air permeability of a preform can be obtained through measuring the pressure profile of gas flow, and (2) that resin permeability is highly correlated with air permeability for the same fiber preform. In this paper, the validity of this method is discussed. Experimental results of gas permeability measurement with defective and defect-free preforms are presented, and quantitative models for correlation of gas permeability versus pressure profile and of gas permeability versus resin permeability are also provided. Finally, the efficacy of the proposed method is illustrated through experimental results.
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5

Lacoste, E., C. Del Borrello, O. Mantaux, and M. Danis. "Processing of Metal Matrix Composites: Bidimensional Numerical Model of the Infiltration of Fibrous Preform by a Pure Metal." In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31447.

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The infiltration process is one of the techniques employed to work out polymer matrix composites (PMC) or metal matrix composites (MMC) and with continuous reinforcement. It consists in injecting the liquid (resin or metal) through a fibrous reinforcement placed in a mould. In the case of the MMC, the fibres and the mould are initially preheated at temperatures lower than the temperature of metal solidification. These thermal conditions induce phenomena of phase change of metal when the metal is in contact with the fibres. These phenomena disturb the flow of metal through the fibrous network. In order to follow the displacement of metal in the preform and take into account of the phase change, a two-dimensional numerical model based on a finite volume formulation was developed, on a very simple geometry.
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Jadhav, Nitesh C., Uday K. Vaidya, Mahesh V. Hosur, John W. Gillespie, and Bruce K. Fink. "Assessment of Flow and Cure Monitoring Using Direct Current and Alternating Current Sensing in Vacuum Assisted Resin Transfer Molding." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0734.

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Abstract Vacuum Assisted Resin Transfer Molding (VARTM) is an emerging manufacturing technique that holds promise as an affordable alternative to traditional autoclave molding and automated fiber placement for producing large scale structural parts. In VARTM, the fibrous preform is laid on a single sided tool, which is then bagged along with the infusion and vacuum lines. The resin is then infused through the preform, which causes simultaneous wetting in its in-plane and transverse directions. An effective sensing technique is essential so that comprehensive information pertaining to the wetting of the preform, arrival of resin at various locations, cure gradients associated with thickness and presence of dry spots may be monitored. In the current work, direct current and alternating current sensing/monitoring techniques were adopted for developing a systematic understanding of resin position and cure on plain weave S2-Glass preforms with Dow Derakane vinyl ester VE 411-350, Shell EPON RSL 2704/2705 and Si-AN epoxy as the matrix systems. The SMARTweave DC sensing system was utilized to conduct parametric studies a) to compare the flow and cure of resin through the stitched and non-stitched preforms, b) influence of sensor positioning, i.e., top, middle and bottom layers, c) influence of positioning of the process accessories, i.e., resin infusion point and vacuum point on the composite panel. The SMARTweave system was found to be sensitive to all the parametric variations introduced in the study. Furthermore, the results obtained from the SMARTweave system were compared to the cure monitored from embedded IDEX dielectric sensors. The results indicate that SMARTweave sensing was a viable alternative to obtaining resin position and cure, and more superior in terms of obtaining global information in contrast to the localized dielectric sensing approach.
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Gebala, Stanislaw. "Examinations Of Phosphor In The Optical Fibre Preform Core." In Optical Fibres and Their Applications, edited by Ryszard S. Romaniuk and Mieczyslaw Szustakowski. SPIE, 1986. http://dx.doi.org/10.1117/12.938958.

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Ribes, J. A., D. D. Wagner, and C. W. Francis. "FIBRIN-STIMULATED RELEASE OF VON WILLEBRAND FACTOR FROM ENDOTHELIAL CELLS IS LINKED TO FIBRINOPEPTIDE B CLEAVAGE." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643772.

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von Willebrand factor (vWf) is synthesized in endothelial cells and stored in specialized organelles, the Weibel-Palade bodies. We have examined the role of fibrin as a potential physiological secretagogue of vWf from Weibel-Palade bodies using indirect immunofluorescence staining of endothelial cells to detect release. Addition of fibrinogen to endothelial cell cultures resulted in the formation of a clot, and this was temporally associated with vWf release. Addition to endothelial cells of preformed fibrin prepared by clotting fibrinogen with thrombin also stimulated release of vWf within 10 minutes. Hirudin inhibition or heat denaturation of clot-bound thrombin abolished most of the thrombin activity but did not diminish release. The role of fibrinopeptide A and B (FPA, FPB) cleavage in stimulating release was examined using reptilase or the venom from A. contortrix to selectively remove FPA or FPB. Release was stimulated by fibrin from which FPB had been cleaved by either thrombin or A. contortrix, while desAA fibrin prepared with Reptilase was an ineffective stimulus. The formation of a stimulatory fibrin clot with the contortrix enzyme, which does not cause release by itself, demonstrates that fibrin stimulation was completely independent of thrombin activity. The capacity to stimulate release was found to be independent of factor XIIIa crosslinking with both crosslinked and noncrosslinked FPB cleaved fibrins demonstrating stimulation. We conclude that fibrin stimulates rapid release of vWf from endothelial cells independent of thrombin activity and may function as a physiologic secretagogue. Furthermore, the stimulating capacity is dependant on cleavage of FPB suggesting that release is mediated by an active site near the N-terminal of the 3 chain or is dependent on a fibrin structure resulting from FPB cleavage.
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Szarska, St, and W. Magierski. "OSEE As The Method Of Determining Of Defect Degree For A Fibre Preforms." In Optical Fibres and Their Applications, edited by Ryszard S. Romaniuk and Mieczyslaw Szustakowski. SPIE, 1986. http://dx.doi.org/10.1117/12.938976.

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Hamidi, Youssef K., Levent Aktas, and M. Cengiz Altan. "Formation of Microscopic Voids in Resin Transfer Molded Composites." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-43837.

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Performance of composite materials usually suffers from process-induced defects such as dry spots or microscopic voids. While effects of void content in molded composites have been studied extensively, knowledge of void morphology and spatial distribution of voids in composites manufactured by resin transfer molding (RTM) remains limited. In this study, through-the-thickness void distribution for a disk-shaped, E-glass/epoxy composite part manufactured by resin transfer molding is investigated. Microscopic image analysis is conducted through-the-thickness of a radial sample obtained from the molded composite disk. Voids are primarily found to concentrate within or adjacent to the fiber preforms. More than 93% of the voids are observed within the preform or in a so-called transition zone, next to a fibrous region. In addition, viod content was found to fluctuate through-the-thickness of the composite. Variation up to 17% of the average viod content of 2.15% is observed through-the-thicknesses of the eight layers studied. Microscopic analysis revealed that average size of voids near the mold surfaces is slightly larger than those located at the interior of the composite. In addition, average size of voids that are located within the fiber preform is observed to be smaller than those located in other regions of the composite. Finally, proximity to the surface is found to have no apparent effect on shape of voids within the composite.
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