Página 18 dos resultados de 205379 itens digitais encontrados em 0.063 segundos

Deep-space laser-ranging missions ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I for astrodynamics and astrometry

Ni, Wei-Tou
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/10/2007
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Deep-space laser ranging will be ideal for testing relativistic gravity, and mapping the solar-system to an unprecedented accuracy. ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I are such missions. ASTROD I is a mission with a single spacecraft; it is the first step of ASTROD with 3 spacecraft. In this talk, after a brief review of ASTROD and ASTROD I, we concentrate of the precision of solar astrodynamics that can be achieved together with implications on astrometry and reference frame transformations. The precision planetary ephemeris derived from these missions together with second post-Newtonian test of relativistic gravity will serve as a foundation for future precise astrometry observations. Relativistic frameworks are discussed from these considerations.; Comment: 5 pages, 2 figures, 2 tables, presented to IAU Symposium No. 248, A Giant Step: from Milli- to Micro-Arcsecond Astrometry (Shanghai, October 15-19, 2007)

An exploration of the effectiveness of artificial mini-magnetospheres as a potential Solar Storm shelter for long term human space missions

Bamford, Ruth; Kellett, Barry; Bradford, John; Todd, Tom N.; Stafford-Allen, Robin; Alves, E. Paulo; Silva, Luis; Collingwood, Cheryl; Crawford, Ian A.; Bingham, Robert
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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In this paper we explore the effectiveness of an artificial mini-magnetosphere as a potential radiation shelter for long term human space missions. Our study includes the differences that the plasma environment makes to the efficiency of the shielding from the high energy charged particle component of solar and cosmic rays, which radically alters the power requirements. The incoming electrostatic charges are shielded by fields supported by the self captured environmental plasma of the solar wind, potentially augmented with additional density. The artificial magnetic field generated on board acts as the means of confinement and control. Evidence for similar behaviour of electromagnetic fields and ionised particles in interplanetary space can be gained by the example of the enhanced shielding effectiveness of naturally occurring "mini-magnetospheres" on the moon. The shielding effect of surface magnetic fields of the order of ~100s nanoTesla is sufficient to provide effective shielding from solar proton bombardment that culminate in visible discolouration of the lunar regolith known as "lunar swirls". Supporting evidence comes from theory, laboratory experiments and computer simulations that have been obtained on this topic. The result of this work is...

The United Nations Human Space Technology Initiative (HSTI): Science Activities

Niu, A.; Ochiai, M.; Haubold, H. J.; Doi, T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/10/2012
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The United Nations Human Space Technology Initiative (HSTI) aims at promoting international cooperation in human spaceflight and space exploration-related activities; creating awareness among countries on the benefits of utilizing human space technology and its applications; and building capacity in microgravity education and research. HSTI has been conducting various scientific activities to promote microgravity education and research. The primary science activity is called 'Zero-gravity Instrument Distribution Project', in which one-axis clinostats will be distributed worldwide. The distribution project will provide unique opportunities for students and researchers to observe the growth of indigenous plants in their countries in a simulated microgravity condition and is expected to create a huge dataset of plant species with their responses to gravity.; Comment: 8 pages. arXiv admin note: text overlap with arXiv:1210.4797

On deformation of electron holes in phase space

Treumann, R. A.; Jaroschek, C. H.; Pottelette, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/10/2008
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This Letter shows that for particularly shaped background particle distributions momentum exchange between phase space holes and the distribution causes acceleration of the holes along the magnetic field. In the particular case of a non-symmetric ring distribution (ring with loss cone) this acceleration is nonuniform in phase space being weaker at larger perpendicular velocities thus causing deformation of the hole in phase space.; Comment: Original MS in EPL style, 1 Figure

Spacecraft Charging and Hazards to Electronics in Space

Mikaelian, Tsoline
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/06/2009
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The interaction of a space system with its orbital environment is a major consideration in the design of any space system, since a variety of hazards are associated with the operation of spacecraft in the harsh space environment. In this brief review, two types of hazards to Earth-orbiting spacecraft are discussed: spacecraft charging and radiation hazards to spacecraft electronics, with emphasis on the natural environmental factors and interactions which contribute to these hazards. Following a summary of the historical eras of spacecraft charging and some observations from experimental satellites: SCATHA, CRRES and DMSP, environmental factors significant to spacecraft charging are discussed, including plasma interactions, electric and magnetic fields and solar radiation. Spacecraft charging depends on the spacecraft geometry, as well as on the characteristics of its orbit, since the natural environment may differ for each type of orbit. Low altitude orbiting satellites (LEO) usually experience less charging effects than high altitude geosynchronous (GEO) satellites, except for low altitude polar orbiting satellites which cross the auroral oval. Basic mechanisms of surface charging, differential charging and internal charging are described. Environmental factors including trapped and transient radiation...

Role of Z-pinches in magnetic reconnection in space plasmas

Olshevsky, Vyacheslav; Lapenta, Giovanni; Markidis, Stefano; Divin, Andrey
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/09/2015
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A widely accepted scenario of magnetic reconnection in collisionless space plasmas is the breakage of magnetic field lines in X-points. In laboratory, reconnection is commonly studied in pinches, current channels embedded into twisted magnetic fields. No model of magnetic reconnection in space plasmas considers both null-points and pinches as peers. We have performed a particle-in-cell simulation of magnetic reconnection in a three-dimensional configuration where null-points are present initially, and Z-pinches are formed during the simulation along the lines of spiral null-points. The non-spiral null-points are more stable than spiral ones, and no substantial energy dissipation is associated with them. On the contrary, turbulent magnetic reconnection in the pinches causes the magnetic energy to decay at a rate of ~1.5% per ion gyro period. Dissipation in similar structures is a likely scenario in space plasmas with large fraction of spiral null-points.

Active Radiation Shield for Space Exploration Missions (ARSSEM)

Battiston, R.; Burger, W. J.; Calvelli, V.; Musenich, R.; Choutko, V.; Datskov, V. I.; Della Torre, A.; Venditti, F.; Gargiulo, C.; Laurenti, G.; Lucidi, S.; Harrison, S.; Meinke, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/09/2012
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One of the major issues to be solved is the protection from the effects of ionizing radiation. Exploration mission, lasting two to three years in space, represents a very significant step from the point of view of radiation protection: both the duration (up to 5 times) and the intensity (up to 5 times) of the exposure to radiation are increased at the same time with respect to mission on the ISS reaching and sometime exceeding professional career limits. In this ARSSEM report, after reviewing the physics basis of the issue of radiation protection in space, we present results based for the first time on full physics simulation to understand the interplay among the the various factors determining the dose absorbed by the astronauts during a long duration mission: radiation composition and energy spectrum, 3D particle propagation through the magnetic field, secondary production on the spacecraft structural materia, dose sensitivity of the various parts of the human body. As first application of this approach, we use this analysis to study a new magnetic configuration based on Double Helix coil and exhibiting a number of interesting features which are suited to active shield application. The study also proposes a technology R&D roadmap for active radiation shield development which would match ESA decadal development strategy for human exploration of space.

Ion Beam Shepherd for Contactless Space Debris Removal

Bombardelli, C.; Pelaez, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/02/2011
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A novel concept for contactless active removal of large space debris is proposed exploiting the use of a high-speed targeted ion beam. The ion beam shepherd spacecraft (IBS) is equipped with an electric propulsion system generating a quasi-neutral plasma pointed against the space debris to remotely modify its orbit without physical contact with the latter. The beam shepherd must be equipped with a secondary propulsion system which counteracts the reaction force exerted by the ion beam hence keeping the distance between the space debris constant throughout the deorbit (or reorbit) process. A preliminary analysis of the concept is provided highlighting the expected performance and the main technologicals challenges. The concept has the potential of making large debris removal operations possible in the near future.; Comment: 13 pages, 5 figures

SAI: a compact atom interferometer for future space missions

Sorrentino, Fiodor; Bongs, Kai; Bouyer, Philippe; Cacciapuoti, Luigi; de Angelis, Marella; Dittus, Hansjorg; Ertmer, Wolfgang; Giorgini, Antonio; Hartwig, Jonas; Hauth, Matthias; Herrmann, Sven; Inguscio, Massimo; Kajari, Endre; K\{ae}nemann, Thorben; L\{
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/03/2010
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Atom interferometry represents a quantum leap in the technology for the ultra-precise monitoring of accelerations and rotations and, therefore, for all the science that relies on the latter quantities. These sensors evolved from a new kind of optics based on matter-waves rather than light-waves and might result in an advancement of the fundamental detection limits by several orders of magnitude. Matter-wave optics is still a young, but rapidly progressing science. The Space Atom Interferometer project (SAI), funded by the European Space Agency, in a multi-pronged approach aims to investigate both experimentally and theoretically the various aspects of placing atom interferometers in space: the equipment needs, the realistically expected performance limits and potential scientific applications in a micro-gravity environment considering all aspects of quantum, relativistic and metrological sciences. A drop-tower compatible prototype of a single-axis atom interferometry accelerometer is under construction. At the same time the team is studying new schemes, e.g. based on degenerate quantum gases as source for the interferometer. A drop-tower compatible atom interferometry acceleration sensor prototype has been designed, and the manufacturing of its subsystems has been started. A compact modular laser system for cooling and trapping rubidium atoms has been assembled. A compact Raman laser module...

Gyrokinetic turbulence: a nonlinear route to dissipation through phase space

Schekochihin, A. A.; Cowley, S. C.; Dorland, W.; Hammett, G. W.; Howes, G. G.; Plunk, G. G.; Quataert, E.; Tatsuno, T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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This paper describes a conceptual framework for understanding kinetic plasma turbulence as a generalized form of energy cascade in phase space. It is emphasized that conversion of turbulent energy into thermodynamic heat is only achievable in the presence of some (however small) degree of collisionality. The smallness of the collision rate is compensated by the emergence of small-scale structure in the velocity space. For gyrokinetic turbulence, a nonlinear perpendicular phase mixing mechanism is identified and described as a turbulent cascade of entropy fluctuations simultaneously occurring at spatial scales smaller than the ion gyroscale and in velocity space. Scaling relations for the resulting fluctuation spectra are derived. An estimate for the collisional cutoff is provided. The importance of adequately modeling and resolving collisions in gyrokinetic simulations is biefly discussed, as well as the relevance of these results to understanding the dissipation-range turbulence in the solar wind and the electrostatic microturbulence in fusion plasmas.; Comment: iop revtex style, 14 pages, 1 figure; submitted to PPCF; invited talk for EPS Conference on Plasma Physics, Crete, June 2008; Replaced to match published version

Relativistic Positioning System in Perturbed Space-time

Kostić, Uroš; Horvat, Martin; Gomboc, Andreja
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/10/2015
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We present a variant of a Global Navigation Satellite System called a Relativistic Positioning System (RPS), which is based on emission coordinates. We modelled the RPS dynamics in a space-time around Earth, described by a perturbed Schwarzschild metric, where we included the perturbations due to Earth multipoles (up to the 6th), the Moon, the Sun, Venus, Jupiter, solid tide, ocean tide, and Kerr rotation effect. The exchange of signals between the satellites and a user was calculated using a ray-tracing method in the Schwarzschild space-time. We find that positioning in a perturbed space-time is feasible and is highly accurate already with standard numerical procedures: the positioning algorithms used to transform between the emission and the Schwarzschild coordinates of the user are very accurate and time efficient -- on a laptop it takes 0.04 s to determine the user's spatial and time coordinates with a relative accuracy of $10^{-28}-10^{-26}$ and $10^{-32}-10^{-30}$, respectively.; Comment: 25 pages

UVMag: Space UV and visible spectropolarimetry

Pertenais, Martin; Neiner, Coralie; Pares, Laurent; Petit, Pascal; Snik, Frans; van harten, Gerard
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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UVMag is a project of a space mission equipped with a high-resolution spectropolarimeter working in the UV and visible range. This M-size mission will be proposed to ESA at its M4 call. The main goal of UVMag is to measure the magnetic fields, winds and environment of all types of stars to reach a better understanding of stellar formation and evolution and of the impact of stellar environment on the surrounding planets. The groundbreaking combination of UV and visible spectropolarimetric observations will allow the scientists to study the stellar surface and its environment simultaneously. The instrumental challenge for this mission is to design a high-resolution space spectropolarimeter measuring the full-Stokes vector of the observed star in a huge spectral domain from 117 nm to 870 nm. This spectral range is the main difficulty because of the dispersion of the optical elements and of birefringence issues in the FUV. As the instrument will be launched into space, the polarimetric module has to be robust and therefore use if possible only static elements. This article presents the different design possibilities for the polarimeter at this point of the project.; Comment: 9 pages, 4 figures, SPIE Conference Astronomical Telescopes + Instrumentation Montreal June 2014

Mechanism controller system for the optical spectroscopic and infrared remote imaging system instrument on board the Rosetta space mission

Rodrigo Montero, Rafael; Castro Marín, J. M.; Brown, V. J. G.; López Jiménez, A. C.; Rodríguez Gómez, Julio
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 176889 bytes; application/pdf
ENG
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The optical, spectroscopic infrared remote imaging system (OSIRIS) is an instrument carried on board the European Space Agency spacecraft Rosetta that will be launched in January 2003 to study in situ the comet Wirtanen. The electronic design of the mechanism controller board (MCB) system of the two OSIRIS optical cameras, the narrow angle camera, and the wide angle camera, is described here. The system is comprised of two boards mounted on an aluminum frame as part of an electronics box that contains the power supply and the digital processor unit of the instrument. The mechanisms controlled by the MCB for each camera are the front door assembly and a filter wheel assembly. The front door assembly for each camera is driven by a four phase, permanent magnet stepper motor. Each filter wheel assembly consists of two, eight filter wheels. Each wheel is driven by a four phase, variable reluctance stepper motor. Each motor, for all the assemblies, also contains a redundant set of four stator phase windings that can be energized separately or in parallel with the main windings. All stepper motors are driven in both directions using the full step unipolar mode of operation. The MCB also performs general housekeeping data acquisition of the OSIRIS instrument...

Comparative analysis of Drosophila melanogaster and Caenorhabditis elegans gene expression experiments in the European Soyuz flights to the International Space Station

Leandro, L. J.; Szewczyk, N. J.; Benguria, Alberto; Herranz, Raúl; Laván, David A.; Medina, F. Javier; Gasset, Gilbert; Loon, J. van; Conley, C. A.; Marco, Roberto
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 187120 bytes; application/pdf
ENG
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The European Soyuz missions have been one of the main routes for conducting scientific experiments onboard the International Space Station, which is currently in the construction phase. A relatively large number of life and physical sciences experiments as well as technology demonstrations have been carried out during these missions. Included among these experiments are the Gene experiment during the Spanish “Cervantes” Soyuz mission and the ICE-1st experiment during the Dutch “Delta” mission. In both experiments, full genome microarray analyses were carried out on RNA extracted from whole animals recovered from the flight. These experiments indicated relatively large scale changes in gene expression levels in response to spaceflight for two popular model systems, Drosophila melanogaster (Gene) and Caenorabditis elegans (ICE-1st). Here we report a comparative analysis of results from these two experiments. Finding orthologous genes between the fruit fly and the nematode was far from straightforward, reducing the number of genes that we could compare to roughly 20% of the full comparative genome. Within this sub-set of the data (2286 genes), only six genes were found to display identical changes between species (decreased) while 1809 genes displayed no change in either species. Future experiments using ground simulation techniques will allow producing a better...

Homogeneous Kaehler and Sasakian structures related to complex hyperbolic space

Gadea, Pedro M.; Oubiña, José A.
Fonte: Cambridge University Press Publicador: Cambridge University Press
Tipo: Artículo Formato: 242390 bytes; application/pdf
ENG
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19 pages, 4 tables.-- MSC2000 codes: Primary 53C30; Secondary 53C25, 53C35, 53C55; We study homogeneous Kaehler structures on a non-compact Hermitian symmetric space and their lifts to homogeneous Sasakian structures on the total space of a principal line bundle over it, and we analyze the case of the complex hyperbolic space.; Partially supported by the Ministry of Science and Innovation, Spain, under Project MTM2008-01386.; Peer reviewed

Síntesi de filtres de microones de banda ampla mitjançant Aggressive Space Maping

Eslava Sabaté, David
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: info:eu-repo/semantics/bachelorThesis; Text Formato: application/pdf
Publicado em //2014 CAT
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En aquest projecte es tracta la síntesis i optimització automatitzada de filtres UWB (Ultra-Wide Band) de Levy, del qual s’adquiriran prèviament els coneixements necessaris per a la seva correcta implementació. A partir d’aquestes dades es realitzarà un programa que sintetitzi de manera automàtica un filtre UWB partint d’especificacions. Això es durà a terme utilitzant la tècnica coneguda com Aggressive Space Mapping (ASM), que permet, mitjançant la modificació de la geometria del circuit en base a l’error de les simulacions EM, la optimització de la estructura inicial.; En este proyecto se trata la síntesis y optimización automatizada de filtros UWB (Ultra-Wide Band) de Levy, del que se adquirirán previamente los conocimientos necesarios para su correcta implementación. A partir de estos datos se realizará un programa que sintetice de manera automática un filtro UWB partiendo de especificaciones. Esto se llevará a cabo utilizando la técnica conocida como Aggressive Space Mapping (ASM), que permite, mediante la modificación de la geometría del circuito en base al error de las simulaciones EM, la optimización de la estructura inicial.; In this project, the automated synthesis and optimization of UWB (Ultra-Wide Band) Levy’s filters is proposed...

On Particle Methods for Parameter Estimation in General State-Space Models

Kantas, Nikolas; Doucet, Arnoud; Singh, Sumeetpal S.; Maciejowski, Jan; Chopin, Nicolas
Fonte: Department of Engineering, University of Cambridge Publicador: Department of Engineering, University of Cambridge
Tipo: Article; published version
EN
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This is the final version of the article. It first appeared from Institute of Mathematical Statistics via http://projecteuclid.org/euclid.ss/1439220716.; Nonlinear non-Gaussian state-space models are ubiquitous in statistics, econometrics, information engineering and signal processing. Particle methods, also known as Sequential Monte Carlo (SMC) methods, provide reliable numerical approximations to the associated state inference problems. However, in most applications, the state-space model of interest also depends on unknown static parameters that need to be estimated from the data. In this context, standard particle methods fail and it is necessary to rely on more sophisticated algorithms. The aim of this paper is to present a comprehensive review of particle methods that have been proposed to perform static parameter estimation in state-space models. We discuss the advantages and limitations of these methods and illustrate their performance on simple models.; N. Kantas was supported by the Engineering and Physical Sciences Research Council (EPSRC) under grant EP/J01365X/1 and programme grant on Control For Energy and Sustainability (EP/G066477/1). S.S. Singh?s research is partly funded by EPSRC under the First Grant Scheme (EP/G037590/1). A. Doucet?s research is partly funded by EPSRC (EP/K000276/1 and EP/K009850/1). N. Chopin?s research is partly by the ANR as part of the ?Investissements d?Avenir? program (ANR-11-LABEX-0047).

On Particle Methods for Parameter Estimation in State-Space Models

Kantas, Nikolas; Doucet, Arnaud; Singh, Sumeetpal S.; Maciejowski, Jan; Chopin, Nicolas
Fonte: Institute of Mathematical Statistics Publicador: Institute of Mathematical Statistics
Tipo: Article; published version
EN
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This is the final version of the article. It first appeared from the Institute of Mathematical Statistics via http://dx.doi.org/10.1214/14-STS511; Nonlinear non-Gaussian state-space models are ubiquitous in statistics, econometrics, information engineering and signal process-ing. Particle methods, also known as Sequential Monte Carlo (SMC) methods, provide reliable numerical approximations to the associated state inference problems. However, in most applications, the state-space model of interest also depends on unknown static parameters that need to be estimated from the data. In this context, standard particle methods fail and it is necessary to rely on more sophisticated algorithms. The aim of this paper is to present a comprehensive review of particle methods that have been proposed to perform static parameter estimation in state-space models. We discuss the advantages and limitations of these methods and illustrate their performance on simple models.; N. Kantas was supported by the Engineering and Physical Sciences Research Council (EPSRC) under grant EP/J01365X/1 and programme grant on Control For Energy and Sustainability (EP/G066477/1). S.S. Singh's research is partly funded by EPSRC under the First Grant Scheme (EP/G037590/1). A. Doucet's research is partly funded by EPSRC (EP/K000276/1 and EP/K009850/1). N. Chopin's research is partly by the ANR as part of the "Investissements d'Avenir" program (ANR-11-LABEX-0047).

Effect of immediate and delayed post space preparation on the apical seal of root canals obturated with different sealers and techniques

Aydemir, Hikmet; Ceylan, Gözlem; Tasdemir, Tamer; Kalyoncuoglu, Elif; Isildak, Ibrahim
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/12/2009 ENG
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During mechanical preparation of the post space, the root canal filling may be twisted or vibrated, depending on several factors associated with the preparation technique and quality of filling. OBJECTIVE: The purpose of this study was to investigate the effect of immediate and delayed post space preparation on the integrity of the apical seal. MATERIAL AND METHODS: Sixty-four extracted human incisors were biomechanically prepared using the step-back technique. Sixty roots were randomly assigned to 6 experimental groups of 10 teeth each and the remaining 4 roots served as positive and negative controls (n=2). The root canals in the different groups were obturated with cold lateral and warm vertical condensation of gutta-percha and one of two sealers (Sealapex and Diaket). Post space was prepared either individually or simultaneously. An insulated copper wire was cut into 10-cm-long pieces. In each canal, one piece was inserted to maintain contact with gutta-percha and extended to the outside as one of two working electrodes. A stainless steel wire with the same dimensions of those of the copper wire, used as the other working electrode, was immersed into the background electrolyte from the center of the bottle. The electrical current between standard and experimental electrodes in canals was measured over a period of 10 days applying a conductivity meter. The Kruskal-Wallis test (p=0.05) determined whether there was a significant difference in microleakage among the groups and the Mann-Whitney U test (p=0.01) was used for multiple comparison grouping variables. RESULTS: The results suggest that only the differences between the root canal filling techniques were statistically significant (p;0.01). CONCLUSION: The quality of the root canal filling is important for the integrity of the apical seal.

Da "Fazenda" à "Comunidade": espaços-tempos que se enraizam na região sisaleira da Bahia; From "Farm" to "Community": space-times rooted in the sisal region of Bahia

Freixo, Alessandra Alexandre
Fonte: Universidade de São Paulo. Faculdade de Filosofia, Letras e Ciências Humanas Publicador: Universidade de São Paulo. Faculdade de Filosofia, Letras e Ciências Humanas
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 30/03/2009 POR
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Neste artigo, busco compreender apluralidade de sentidos atribuídos à comunidade naregião sisaleira a partir de dois pontos de partida:primeiramente, pensando a comunidade como umespaço-tempo constituído no início da década de1970, que marca o início de um processo de mobi-lização social; em segundo lugar, compreendendo acomunidade como uma localidade, à medida que osprocessos de mobilização social ocorrem no espaçogeográfico da fazenda, que passa a coincidir coma comunidade, que se torna referência não apenasdo “trabalho social”, mas também como um lugar.Neste sentido, podemos supor um caminho “da fa-zenda à comunidade”, como um processo de pro-dução de um novo espaço-tempo. Para tal análisedos sentidos de comunidade na região, tomei comoprincipal suporte as narrativas dos mais velhos mo-radores das localidades em estudo, bem como delideranças comunitárias e militantes do Movimentode Evangelização Rural (MER) que atuaram na dé-cada de 1970.; This article aims at understanding theplurality of meanings assigned to the “community”in the sisal region from two points of departure: thecommunity is firstly considered as a space-time for-med at the beginning of the 1970’s, marking the be-ginning of a process of social mobilization; it is thenunderstood as a locality...