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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Instrument characterization of the THEMIS EFI

Lindgren, Sara January 2011 (has links)
In March 2007 five satellites were launched as part of the NASA mission THEMIS. The aim of the mission is to answer the unknown questions regarding the onset of substorms. THEMIS data has also been used within other research fields. Today many scientists aim to investigate wave phenomena, such as whistler waves, wave interactions in the radiation belts and general turbulence in the magnetosphere and the solar wind. These processes occur at intermediate frequencies (a few hundreds of Hertz). Correct and reliable results require good knowledge of the frequency response,  the so called transfer function, for the electric field instrument (EFI). Post-launch calibrations have given good knowledge of the instrument's response at high and low frequencies. However, at intermediate frequencies (50-3000 Hz) the transfer function has only been determined via calculations/simulations and not yet obtained from data collected in space. Moreover, the transfer function changes substantially in this range, as the instrument transitions from a resistive low-frequency coupling to a capacitive high-frequency coupling. The transition is known as the RC roll-off. In this thesis, data from different regions and with different electrical settings have been analyzed to estimate the EFI sensors' sheath impedance and transfer function. Data have been collected during July 2009 and March 2011. From the first period, I-V curves where extracted for four different regions (i.e. with different plasma conditions) and their associated sheath impedance calculated. I-V curves are graphical representations of how the voltage differs with the changed bias current. From the sheath impedance and the measured free-space capacitance the RC roll-off can been directly calculated. An experiment was also conducted in March 2011 where the instrument was run in a special mode designed to measure the relative transfer function with the probes run at different bias setting, yielding different sheath impedances. The analysis of the I-V curves and relative transfer function show similar results, which clearly differ from the earlier believed values. Values for the sheath impedance are lower (4-6 MΩ) than the expected (30 MΩ) and depend on the usher setting. The usher is an electronic device which should shield the sensor from the photoelectron produced by illumination of the preamplifier. This lower sheath resistance implies higher than expected RC roll-off frequency, a result which is confirmed by the results from the relative transfer function. The roll-off is between 2-3 kHz, compared to the 400-500 Hz assumed prior to this study based on the assumption of a sheath impedance of around 30 MΩ.
2

Simulating explosive foil initiators : Computer models for the ignition process / Simulering av explosiva foliedetonatorer : Datormodeller för initeringsprocessen

Fasth, Alexander January 2024 (has links)
The exploding foil initiator (EFI) is a high voltage detonator used to initiate explosions. It is designed to improvesafety standards by lowering the risk of accidental detonation and in doing so allows for in-line integration in, forexample, weapon systems that minimizes their complexity and thus reduces the number of possible failures. It ishighly reliable in terms of timing and avoids that functionality of the detonator deteriorates over time, which has beena problem in earlier designs of detonators. This thesis aims to develop an understanding of each part of the initiationprocess by means of computer simulations. The proportions of the electrically conducting bridge is varied in order tofind relations that optimize the design. Success depends on the simulated pressure generated inside a hexanitrostilbene(HNS) primer.The results showed that increasing the dimensions of the bridge greatly affects the pressure produced in the primer,but its proportions were still important. Unfortunately the simulations of the electrical explosion and the accelerationof the flyer suffered from convergence issues that rendered the flyer’s velocity graphs incomplete. But even with theseshortcomings, thanks to empirical data from earlier studies that analysed EFI prototypes, it was possible to makepredictions about the success of various set ups. The information gathered in this thesis should serve as a foundationfor future development of computer models of the EFI technology that will aid the production of prototypes that meetthe specific requirements.i / Den explosiva folieinitieraren (EFI) är en högspänningsdetonator som används för att initiera explosiva förlopp. Denär designad för att förbättra säkerheten genom att sänka risken för oavsiktlig detonering och till följd av detta möjligörför in-line integrering i, till exempel, vapensystem. Detta minimerar komplexiteten av sådanna system och sänker antaletmöjliga fel som kan uppstå. Denna teknolgi är högst pålitlig när det gäller timing och undviker att detonatorns funktionförsämras över tid, vilket har varit ett problem i tidigare konstruktioner av detonatorer. Denna avhandling syftar tillatt utveckla en förståelse för varje del av initieringsprocessen genom datorsimuleringar. Proportionerna av den elektrisktledande bryggan varierades för att hitta relationer som optimerar designen. Framgången beror på det simulerade trycketsom genereras inuti en primer av det explosiva materialet hexanitrostilben (HNS).Resultaten visade att ökade dimensioner på bryggan kraftigt påverkar trycket som produceras i primern, men dessproportioner var fortfarande viktiga. Tyvärr led simuleringarna av den elektriska explosionen och accelerationen avflyern av konvergensproblem som gjorde att flyerns hastighetsgrafer blev ofullständiga. Men även med dessa brister,tack vare empiriska data från tidigare studier som analyserade EFI-prototyper, var det möjligt att göra förutsägelserom framgången för olika uppsättningar. Informationen som samlats in i denna avhandling bör tjäna som en grund förframtida utveckling av dator modeller av EFI-teknologi som kommer att underlätta produktionen av prototyper somuppfyller specifika krav.ii
3

En empirisk granskning av korrelationen mellan handelsliberalism och ekonomisk tillväxt : Finns ett samband mellan handelsliberalism och ekonomisk tillväxt i länder i Mellanöstern & Asien?

Allan, Kadir, Gemvall, Maria January 2017 (has links)
The purpose of the thesis has been to investigate whether there is a link between trade liberalism and economic growth in the Asian countries. Previous research has pointed out that correlation exists between these variables, but there have also been other researchers who criticized such a relationship. We discovered that economic growth studies had previously been conducted where countries in Asia were included. This motivated us to carry out our study as our research hopefully helps to replenish existing knowledge gap. In the study, we have used cross-sectional regression analysis for 30 Asian countries where data were collected for 1990-2000. Our dependent variable in our regression is average GDP per capita, which also defines growth. We have used two independent variables as main variables, trade volume and economic freedom index. Our analysis shows that the majority of the variables in the study have a positive significant relation to economic growth. Keywords: economic growth, trade liberalism, trade, GDP / capita, EFI, direct investment, import, export.
4

Design And Analysis Of A High Voltage Exploding Foil Initiator For Missile Systems

Yilmaz, Muhammed Yusuf 01 February 2013 (has links) (PDF)
Increasing insensitivity demands on designing and producing munitions necessitates utilizing primarily insensitive initiation trains specifically in missile systems. Exploding Foil Initiator (EFI) is a high voltage detonator that is used as the initiation elementof rocket motor and warhead initiation trains of modern insensitive missile systems. In this thesis, EFI prototypes are designed and manufactured with the knowledge gained from detailed literature studies. An experimental setup is constructed including firing and testing means for EFI prototypes. That experimental setup is capable of firing EFI prototypes from 500 volts to 3000 volts voltage range. Besides, it allows measuring electrical characteristics like current and voltage traces and average velocity of the flyer plates of these prototypes.Using EFI prototypes,detonation tests of HNS &ndash / IV and PBXN &ndash / 5 explosive pellets are carried out.Function times and detonation outputs of the prototypesare measured with the same experimental setup. A numerical study which predicts electrical performance of EFI prototypes and impact characteristics of flyer plates are carried out. Numerical code is validated with the experimental results.
5

Optimal Combination of Reduction Methods in Structural Mechanics and Selection of a Suitable Intermediate Dimension / Optimale Kombination von strukturmechanischen Modellreduktionsverfahren und Wahl einer geeigneten Zwischendimension

Paulke, Jan 19 August 2014 (has links) (PDF)
A two-step model order reduction method is investigated in order to overcome problems of certain one-step methods. Not only optimal combinations of one-step reductions are considered but also the selection of a suitable intermediate dimension (ID) is described. Several automated selection methods are presented and their application tested on a gear box model. The implementation is realized using a Matlab-based Software MORPACK. Several recommendations are given towards the selection of a suitable ID, and problems in Model Order Reduction (MOR) combinations are pointed out. A pseudo two-step is suggested to reduce the full system without any modal information. A new node selection approach is proposed to enhance the SEREP approximation of the system’s response for small reduced representations. / Mehrschrittverfahren der Modellreduktion werden untersucht, um spezielle Probleme konventioneller Einschrittverfahren zu lösen. Eine optimale Kombination von strukturmechanischen Reduktionsverfahren und die Auswahl einer geeigneten Zwischendimension wird untersucht. Dafür werden automatische Verfahren in Matlab implementiert, in die Software MORPACK integriert und anhand des Finite Elemente Modells eines Getriebegehäuses ausgewertet. Zur Auswahl der Zwischendimension werden Empfehlungen genannt und auf Probleme bei der Kombinationen bestimmter Reduktionsverfahren hingewiesen. Ein Pseudo- Zweischrittverfahren wird vorgestellt, welches eine Reduktion ohne Kenntnis der modalen Größen bei ähnlicher Genauigkeit im Vergleich zu modalen Unterraumverfahren durchführt. Für kleine Reduktionsdimensionen wird ein Knotenauswahlverfahren vorgeschlagen, um die Approximation des Frequenzganges durch die System Equivalent Reduction Expansion Process (SEREP)-Reduktion zu verbessern.
6

Optimal Combination of Reduction Methods in Structural Mechanics and Selection of a Suitable Intermediate Dimension: Optimal Combination of Reduction Methods in Structural Mechanics and Selection of a Suitable Intermediate Dimension

Paulke, Jan 08 May 2014 (has links)
A two-step model order reduction method is investigated in order to overcome problems of certain one-step methods. Not only optimal combinations of one-step reductions are considered but also the selection of a suitable intermediate dimension (ID) is described. Several automated selection methods are presented and their application tested on a gear box model. The implementation is realized using a Matlab-based Software MORPACK. Several recommendations are given towards the selection of a suitable ID, and problems in Model Order Reduction (MOR) combinations are pointed out. A pseudo two-step is suggested to reduce the full system without any modal information. A new node selection approach is proposed to enhance the SEREP approximation of the system’s response for small reduced representations.:Contents Kurzfassung..........................................................................................iv Abstract.................................................................................................iv Nomenclature........................................................................................ix 1 Introduction........................................................................................1 1.1 Motivation........................................................................................1 1.2 Objectives........................................................................................1 1.3 Outline of the Thesis........................................................................2 2 Theoretical Background.......................................................................3 2.1 Finite Element Method......................................................................3 2.1.1 Modal Analysis...............................................................................4 2.1.2 Frequency Response Function.......................................................4 2.2 Model Order Reduction.....................................................................5 2.3 Physical Subspace Reduction Methods.............................................7 2.3.1 Guyan Reduction...........................................................................7 2.3.2 Improved Reduced System Method...............................................8 2.4 Modal Subspace Reduction Methods...............................................10 2.4.1 Modal Reduction...........................................................................11 2.4.2 Exact Modal Reduction..................................................................11 2.4.3 System Equivalent Reduction Expansion Process.........................13 2.5 Krylov Subspace Reduction Methods...............................................14 2.6 Hybrid Subspace Reduction Methods..............................................15 2.6.1 Component Mode Synthesis........................................................16 2.6.2 Hybrid Exact Modal Reduction......................................................19 2.7 Model Correlation Methods.............................................................21 2.7.1 Normalized Relative Frequency Difference...................................21 2.7.2 Modified Modal Assurance Criterion.............................................22 2.7.3 Pseudo-Orthogonality Check.......................................................22 2.7.4 Comparison of Frequency Response Function.............................23 3 Selection of Active Degrees of Freedom............................................25 3.1 Non-Iterative Methods...................................................................26 3.1.1 Modal Kinetic Energy and Variants..............................................26 3.1.2 Driving Point Residue and Variants..............................................27 3.1.3 Eigenvector Component Product..................................................28 3.2 Iterative Reduction Methods...........................................................29 3.2.1 Effective Independence Distribution.............................................29 3.2.2 Mass-Weighted Effective Independence.......................................32 3.2.3 Variance Based Selection Method.................................................33 3.2.4 Singular Value Decomposition Based Selection Method................34 3.2.5 Stiffness-to-Mass Ratio Selection Method.....................................34 3.3 Iterative Expansion Methods...........................................................35 3.3.1 Modal-Geometrical Selection Criterion...........................................36 3.3.2 Triaxial Effective Independence Expansion...................................36 3.4 Measure of Goodness for Selected Active Set..................................39 3.4.1 Determinant and Rank of the Fisher Information Matrix................39 3.4.2 Condition Number of the Partitioned Modal Matrix........................40 3.4.3 Measured Energy per Mode..........................................................40 3.4.4 Root Mean Square Error of Pseudo-Orthogonality Check.............41 3.4.5 Eigenvalue Comparison................................................................41 4 Two-Step Reduction in MORPACK.......................................................42 4.1 Structure of MORPACK.....................................................................42 4.2 Selection of an Intermediate Dimension.........................................43 4.2.1 Intermediate Dimension Requirements........................................44 4.2.2 Implemented Selection Methods..................................................45 4.2.3 Recommended Selection of an Intermediate Dimension...............48 4.3 Combination of Reduction Methods.................................................49 4.3.1 Overview of All Candidates..........................................................50 4.3.2 Combinations with Modal Information.........................................54 4.3.3 Combinations without Modal Information....................................54 5 Applications........................................................................................57 5.1 Gear Box Model...............................................................................57 5.2 Selection of Additional Active Nodes................................................58 5.3 Optimal Intermediate Dimension......................................................64 5.4 Two-Step Model Order Reduction Results........................................66 5.5 Comparison to One-Step Model Order Reduction Methods..............70 5.6 Comparison to One-Step Hybrid Model Order Reduction Methods...72 5.7 Proposal of a New Approach for Additional Node Selection..............73 6 Summary and Conclusions...................................................................77 7 Zusammenfassung und Ausblick..........................................................79 Bibliography............................................................................................81 List of Tables..........................................................................................86 List of Figures.........................................................................................88 A Appendix.............................................................................................89 A.1 Results of Two-Step Model Order Reduction.....................................89 A.2 Data CD............................................................................................96 / Mehrschrittverfahren der Modellreduktion werden untersucht, um spezielle Probleme konventioneller Einschrittverfahren zu lösen. Eine optimale Kombination von strukturmechanischen Reduktionsverfahren und die Auswahl einer geeigneten Zwischendimension wird untersucht. Dafür werden automatische Verfahren in Matlab implementiert, in die Software MORPACK integriert und anhand des Finite Elemente Modells eines Getriebegehäuses ausgewertet. Zur Auswahl der Zwischendimension werden Empfehlungen genannt und auf Probleme bei der Kombinationen bestimmter Reduktionsverfahren hingewiesen. Ein Pseudo- Zweischrittverfahren wird vorgestellt, welches eine Reduktion ohne Kenntnis der modalen Größen bei ähnlicher Genauigkeit im Vergleich zu modalen Unterraumverfahren durchführt. Für kleine Reduktionsdimensionen wird ein Knotenauswahlverfahren vorgeschlagen, um die Approximation des Frequenzganges durch die System Equivalent Reduction Expansion Process (SEREP)-Reduktion zu verbessern.:Contents Kurzfassung..........................................................................................iv Abstract.................................................................................................iv Nomenclature........................................................................................ix 1 Introduction........................................................................................1 1.1 Motivation........................................................................................1 1.2 Objectives........................................................................................1 1.3 Outline of the Thesis........................................................................2 2 Theoretical Background.......................................................................3 2.1 Finite Element Method......................................................................3 2.1.1 Modal Analysis...............................................................................4 2.1.2 Frequency Response Function.......................................................4 2.2 Model Order Reduction.....................................................................5 2.3 Physical Subspace Reduction Methods.............................................7 2.3.1 Guyan Reduction...........................................................................7 2.3.2 Improved Reduced System Method...............................................8 2.4 Modal Subspace Reduction Methods...............................................10 2.4.1 Modal Reduction...........................................................................11 2.4.2 Exact Modal Reduction..................................................................11 2.4.3 System Equivalent Reduction Expansion Process.........................13 2.5 Krylov Subspace Reduction Methods...............................................14 2.6 Hybrid Subspace Reduction Methods..............................................15 2.6.1 Component Mode Synthesis........................................................16 2.6.2 Hybrid Exact Modal Reduction......................................................19 2.7 Model Correlation Methods.............................................................21 2.7.1 Normalized Relative Frequency Difference...................................21 2.7.2 Modified Modal Assurance Criterion.............................................22 2.7.3 Pseudo-Orthogonality Check.......................................................22 2.7.4 Comparison of Frequency Response Function.............................23 3 Selection of Active Degrees of Freedom............................................25 3.1 Non-Iterative Methods...................................................................26 3.1.1 Modal Kinetic Energy and Variants..............................................26 3.1.2 Driving Point Residue and Variants..............................................27 3.1.3 Eigenvector Component Product..................................................28 3.2 Iterative Reduction Methods...........................................................29 3.2.1 Effective Independence Distribution.............................................29 3.2.2 Mass-Weighted Effective Independence.......................................32 3.2.3 Variance Based Selection Method.................................................33 3.2.4 Singular Value Decomposition Based Selection Method................34 3.2.5 Stiffness-to-Mass Ratio Selection Method.....................................34 3.3 Iterative Expansion Methods...........................................................35 3.3.1 Modal-Geometrical Selection Criterion...........................................36 3.3.2 Triaxial Effective Independence Expansion...................................36 3.4 Measure of Goodness for Selected Active Set..................................39 3.4.1 Determinant and Rank of the Fisher Information Matrix................39 3.4.2 Condition Number of the Partitioned Modal Matrix........................40 3.4.3 Measured Energy per Mode..........................................................40 3.4.4 Root Mean Square Error of Pseudo-Orthogonality Check.............41 3.4.5 Eigenvalue Comparison................................................................41 4 Two-Step Reduction in MORPACK.......................................................42 4.1 Structure of MORPACK.....................................................................42 4.2 Selection of an Intermediate Dimension.........................................43 4.2.1 Intermediate Dimension Requirements........................................44 4.2.2 Implemented Selection Methods..................................................45 4.2.3 Recommended Selection of an Intermediate Dimension...............48 4.3 Combination of Reduction Methods.................................................49 4.3.1 Overview of All Candidates..........................................................50 4.3.2 Combinations with Modal Information.........................................54 4.3.3 Combinations without Modal Information....................................54 5 Applications........................................................................................57 5.1 Gear Box Model...............................................................................57 5.2 Selection of Additional Active Nodes................................................58 5.3 Optimal Intermediate Dimension......................................................64 5.4 Two-Step Model Order Reduction Results........................................66 5.5 Comparison to One-Step Model Order Reduction Methods..............70 5.6 Comparison to One-Step Hybrid Model Order Reduction Methods...72 5.7 Proposal of a New Approach for Additional Node Selection..............73 6 Summary and Conclusions...................................................................77 7 Zusammenfassung und Ausblick..........................................................79 Bibliography............................................................................................81 List of Tables..........................................................................................86 List of Figures.........................................................................................88 A Appendix.............................................................................................89 A.1 Results of Two-Step Model Order Reduction.....................................89 A.2 Data CD............................................................................................96
7

Entreprenörskapets, Företagandets och det Innovativa tänkandets Läroplansdidaktik (EFID) i Gymnasieskolan : En fallstudie av Sveagymnasium

Glassér, Charlotte January 2017 (has links)
År 2010 fick Sverige en ny skollag för grund- och gymnasieskolan och år 2011 kom dess relaterade nya läroplaner. I styrdokumenten för gymnasieskolan formuleras och betonas starkt ”entreprenörskap, företagande och innovation”, som politiska utbildnings- och lärandemål, vilka ska genomsyra alla utbildningsår och ämnen. Syftet med denna studie är att bredda och fördjupa forskningen och kunskapen om hur läroplanen för gymnasiet 2011 transformerats och realiserats, vad avser utbildning och didaktiska praktiker i ”entreprenörskap, företagande och innovativt tänkande” (EFI Lgy 2011). Med en abduktiv, och hermeneutisk forskningsdesign och fallbeskrivning som metodansats kartläggs, analyseras och beskrivs hur skolledningen och kollegiet på den utvalda skolan ”Sveagymnasium”, och dess erbjudna treåriga högskoleförberedande utbildningsprogram, har transformerat och realiserat läroplanens direktiv om utbildning och lärande i EFI Lgy2011 under perioden 2012–2016. Studiens huvudsakliga bidrag är fallbeskrivningen av Entreprenörskapets, Företagandets och det Innovativa tänkandets läroplansdidaktik (EFID) på Sveagymnasium. Fallbeskrivningen förmedlar förståelsen av en skola där det föreligger formell och fastställd samordning mellan lärandemålen i entreprenörskap, företagande och innovativt tänkande (EFI Lgy 2011), relaterad schemabunden- och ämnesintegrerad undervisning, bedömning och betygssättning. Detta är den empiriska grunden för deninitierade teoribildningen och forskningen om Entreprenörskapets, Företagandets och det Innovativa tänkandets Didaktik (EFID Lgy 2011). Fallstudien kan även användas som pedagogiskt redskap i utbildande och skolutvecklande syfte. Studien avser främst att bidra till den empiriska, läroplansdidaktiska, forskningen och dess teoribildning med en sociokulturell och redskapsmedierad betraktelselins
8

Entwicklung und Evaluation eines Unterrichtskonzeptes für computergestütztes kooperatives Lernen

Holl, Berit 07 March 2004 (has links) (PDF)
In der Dissertationsschrift wird die Entwicklung und Evaluation eines Unterrichtskonzeptes für computergestütztes kooperatives Lernen am beruflichen Gymnasium für Informations- und Kommunikationstechnologie beschrieben. Das Konzept für Computer Supported Cooperative Learning (CSCL) wurde im Rahmen des sächsischen Landesschulversuches "Einführung der Fachrichtung Informations- und Kommunikationstechnologie am beruflichen Gymnasium im Freistaat Sachsen" in Zusammenarbeit mit der Technischen Berufsschule Zürich erprobt. In der Dissertationsschrift werden Fachbegriffe der Didaktik der Informatik präzisiert. Desweiteren sind Forschungsmethoden, quantitative und qualitative Untersuchungsergebnisse sowie deren Auswertung insbesondere zur CSCL-Handlungskompetenz enthalten.
9

Printing colour hard proofs using EFI Colorproof XF v. 3.1 and Photoshop CS3, and production substrates.

Johansson, Nils January 2009 (has links)
EFI Colorproof XF was found to be more convenient from a user’s aspect, and had features which are covered in the ISO 12647-7 standard (e.g. the ability to simulate screening and print margin information), which Photoshop CS3 lacked. None of the proofing systems distinguished itself in a clear way from the other; sometimes, on certain substrates, Photoshop CS3 produced most accurate colours, sometimes EFI Colorproof XF did. Further investigations need to be carried out to tell more exactly which system produce most accurate colours. Only 6 out of 34 simulation-combinations had colours within the tolerances in the standard. The result also shows that the production substrates should not be used as proofing substrates. Instead the proofing papers especially made for ink jet should be used to obtain more colour-accurate prints.
10

Tradição e inovação: sentidos de currículo que se hibridizam nos discursos sobre o ensino de Ciências nos anos iniciais do Ensino Fundamental / Curriculum meanings that pervade the discourse on Science teaching at the early years of Elementary school

Talita Vidal Pereira 17 August 2011 (has links)
Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Este estudo se insere em uma abordagem Pós-estruturalista. Nele, o conceito de discurso desenvolvido por Laclau é utilizado como categoria de análise para investigar o processo de legitimação do saber científico. O conceito de recontextualização por hibridismo proposto por Lopes (2005; 2006a) orienta a análise dos discursos produzidos nos diferentes contextos de produção curricular, a partir da abordagem do ciclo de políticas desenvolvida por Bowe, Ball e Gold (1992)e Ball (1994). No trabalho, são identificadas as demandas articuladas nos discursos de uma comunidade de pesquisadores que têm investigado o ensino de ciências nos anos iniciais do Ensino Fundamental. O estudo também apresenta uma reflexão produzida a partir de dados reunidos em uma pesquisa de cunho etnográfico,realizada em duas escolas da rede municipal de ensino do município do Rio de Janeiro. As análises indicam que o discurso educacional sobre o ensino de ciências expressa sentidos em disputa que oscilam entre a incorporação de novos paradigmas de ciência e de currículo e a manutenção de marcas que procuram preservar a ciência como conhecimento superior, contribuindo para a reafirmação dos princípios racionais que estão na base de constituição da escola como instituição da modernidade e associadas ao processo de hegemonização desse saber. / This study falls within a Post-structuralist approach. In this study, Laclau's concept of discourse is used as an analysis category to investigate the legitimization process of scientific knowledge. The concept of recontextualization by hybridism proposed by Lopes (2005; 2006a) guides the analysis of the discourses produced in the different contexts of curriculum production based on the policy cycle approach developed by Bowe, Ball and Gold (1992) and Ball (1994). This study identifies the demands voiced in the discourse of a researchers community that has been investigating science teaching at the initial years of Elementary School. The study also presents some reflection on the data gathered in an ethnographic research conducted in two schools from the Rio de Janeiro City school system. The analysis show that the educational discourse on science teaching conveys disputing meanings that range from the incorporation of new paradigms of science and curriculum to the maintenance of marks that seek to preserve science as a superior form of knowledge. Such marks contribute to the reaffirmation of the rational principles that form the basis of the school as a modern institution and are associated with the process of making this knowledge hegemonic.

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