Spelling suggestions: "subject:"massive"" "subject:"assive""
281 |
Caractérisation des discontinuités dans des ouvrages massifs en béton par la diagraphie électrique de résistivité / Characterization of discontinuities inside massive concrete structures with electrical resistivity loggingTaillet, Elodie 17 December 2013 (has links)
Les discontinuités sont préjudiciables à la pérennité des structures en béton. Les méthodes non-destructives sont bien développées pour l’étude des altérations en surface, mais peu de techniques sont adaptées à la caractérisation de défauts dans la masse. Dans cette thèse, des mesures de résistivité électrique sont réalisées pour l’étude des discontinuités (fissures, joints, interfaces) au sein des ouvrages massifs en béton par l’intermédiaire des forages préexistants. La technique utilisée est la diagraphie électrique de résistivité en dispositif normal. Une première approche numérique (éléments finis) permet d’appréhender les corrections à apporter sur les mesures. Puis l’étude des paramètres d'ouverture, de contraste entre la résistivité de la discontinuité et du béton, et d'extension permet de proposer une méthode d’inversion des mesures pour la caractérisation de l’endommagement. Des essais sur des ouvrages hydrauliques sont réalisés afin de définir la méthodologie de mesure sur site. Les mesures sont ensuite confrontées à la méthode d’inversion pour la valider. / Discontinuities are one of the most harmful damage to the durability of concrete structures. The non-destructive methods appear to be effective for the detection and the location of surface cracks but they might be unsuitable for investigation of massive concrete body. In this thesis, the electrical resistivity measurements are made for the study of cracks and discontinuities (concrete joints, interfaces ...) in massive concrete structures by preexisting boreholes. The study is based on a first numerical approach (finite elements) to understand the corrections on data. Then the study of the aperture, the resistivity contrast between the discontinuity and the concrete, and the extension provide a method for the inversion of measures to characterize the damage. The tests on hydraulic structures are carried out to define the methodology for on measurement site. The measurements are then compared to the inversion method to validate it.
|
282 |
Využití metody paralelního sekvenování při stanovování zešikmení X inaktivace / Use of massive parallel sequencing in determination of skewed X inactivationVeselková, Tereza January 2016 (has links)
Skewed X chromosome inactivation has been often studied as a possible factor that influences manifestation of X-linked diseases in heterozygous women. Yet the association between phenotype and degree of skewing stays unclear for most disorders. Current works rely mostly on methods that are based on methyl-sensitive restriction while determining the X inactivation pattern and mainly the HUMARA assay which investigates the methylation profile in the AR gene. However those methods have some known disadvantages and therefore we are still seeking new methodical approaches. We used DNA isolated from whole blood and in some cases also buccal swabs to asses X inactivation patterns in 54 women using methylation-based methods for loci AR, CNKSR2 and RP2. Transcription-based assay was utilized to evaluate skewing of X inactivation in 32 of those women, whose samples were available for RNA extraction, using massive parallel sequencing and polymorphisms LAMP2 c.156A>T, IDS c.438C>T and ABCD1 c.1548G>A. Partly thanks to almost no stuttering during PCR the RP2 locus was the most informative in our study (71 % of women) and approximately the same number of women (69 %) were informative for the HUMARA assay. However when comparing the results of those two methods we determined difference greater than 10 % in...
|
283 |
Flash-Annealing of Cu-Zr-Al-based Bulk Metallic GlassesKosiba, Konrad 29 May 2017 (has links) (PDF)
(Bulk) metallic glasses ((B)MGs) are known to exhibit the highest yield strength of any metallic material (up to 5GPa), and show an elastic strain at ambient conditions, which is about ten times larger than that of crystalline materials. Despite these intriguing mechanical properties, BMGs are not used as structural materials in service, so far. The major obstacle is their inherent brittleness, which results from severe strain localization in so-called shear bands. MGs fail due to formation and propagation of shear bands. A very effective way to attenuate the brittle behaviour is to incorporate crystals into the glass. The resulting BMG composites exhibit high strength as well as plasticity. Cu-Zr-Al-based BMG composites are special to that effect, since they combine high strength, plasticity and work-hardening.
They are comprised of the glass and shape-memory B2 CuZr crystals, which can undergo a deformation-induced martensitic transformation. The work-hardening originates from the martensitic transformation and overcompensates the work-softening of the glass. The extent of the plasticity of BMG composites depends on the volume fraction, size and particularly on the distribution of the B2 CuZr crystals. Nowadays, it is very difficult, if not impossible to prepare BMG composites with uniformly distributed crystals in a reproducible manner by melt-quenching, which is the standard preparation method. Flash-annealing of BMGs represents a new approach to overcome this deficiency in the preparation of BMG composites and is the topic of the current thesis. Cu46Zr46Al8 and Cu44Zr44Al8Hf2Co2 BMGs were flash-annealed and afterwards investigated in terms of phase formation, crystallization kinetics and mechanical properties. Flash-annealing is a process, which is characterized by the rapid heating of BMGs to predefined temperatures followed by instantaneous quenching. A temperature-controlled device was succesfully developed and built. The Cu-Zr-Al-based BMGs can be heated at rates ranging between 16 K/s and about 200 K/s to temperatues above their melting point. Rapid heating is followed by immediate quenching where cooling rates of the order of 1000 K/s are achieved.
As a BMG is flash-annealed, it passes the glass-transition temperature, Tg, and transforms to a supercooled liquid. Further heating leads to its crystallization and the respective temperature, the crystallization temperature, Tx, divides the flash-annealing of BMGs into two regimes:
(1) sub-Tx-annealing and (2) crystallization.
The structure of the glass exhibits free volume enhanced regions (FERs) and quenched-in nuclei. Flash-annealing affects both heterogeneities and hence the structural state of the glass. FERs appear to be small nanoscale regions and they can serve as initiation sites for shear bands. Flash-annealing of Cu-Zr-Al-based BMGs to temperatures below Tg leads to structural relaxation, the annihilation of FERs and the BMG embrittles. In contrast, the BMG rejuvenates, when flash-annealed to temperatures of the supercooled liquid region (SLR). Rejuvenation is associated with the creation of FERs. Compared to the as-cast state, rejuvenated BMGs show an improved plasticity, due to a proliferation of shear bands, which are the carrier of plasticity in MGs. Flash-annealing enables to probe the influence of the free volume in bulk samples on their mechanical properties, which could not be studied, yet.
In addition, B2 CuZr nanocrystals precipitate during the deformation of flash-annealed Cu44Zr44Al8Hf2Co2 BMGs. Deformation-induced nanocrystallization does not occur for the present as-cast BMGs. Flash-annealing appears to stimulate the growth of quenched-in nuclei, which are subcritical in size and can also dissolve, once the BMG is heated to temperatures in the SLR. Rejuvenation represents a disordering process, whereas the growth of quenched-in nuclei is associated with ordering. There is a competition between both processes during flash-annealing. The ordering seems to lead to a “B2-like” clustering of the medium range of Cu44Zr44Al8Hf2Co2 BMGs with increasing heating duration. So far, there does not exist another method to manipulate the MRO of BMGs. If Cu44Zr44Al8Hf2Co2 BMGs are flash-annealed to temperatures near Tx, most likely compressive resiudal stresses develop near the surface, which is cooled faster than the interior of the BMG specimen. They hinder the propagation of shear bands and increase the plasticity of flash-annealed BMGs in addition to rejuvenation and deformation-induced nanocrystallization.
If BMGs are heated to temperatures above Tx, they start to crystallize. Depending on the exact temperature to which the BMG is flash-annealed and subsequently quenched, one can induce controlled partial crystallization. Consequently, BMG composites can be prepared. Both Cu-Zr-Al-based BMGs are flash-annealed at various heating rates to study the phase formation as a function of the heating rate. In addition, Tg and Tx are identified for each heating rate, so that a continuous heating transformation diagram is constructed for both glass-forming compositions. An increasing heating rate kinetically constrains the crystallization process, which changes from eutectic (Cu10Zr7 and CuZr2) to polymorphic (B2 CuZr). If the Cu-Zr-Al-based BMGs are heated above a critical heating rate, exclusively B2CuZr crystals precipitate, which are metastable at these temperatures. Thus, flash-annealing of Cu46Zr46Al8 and Cu44Zr44Al8Hf2Co2 BMGs followed by quenching enables the preparation of B2 CuZr BMG composites. The B2 precipitates are small, high in number and uniformly distributed when compared to conventional BMG composites prepared by melt-quenching. Such composite microstructures allow the direct observation of crystal sizes and numbers, so that crystallization kinetics of deeply supercooled liquids can be studied as they are flash-annealed. The nucleation kinetics of devitrified metallic glass significantly diverge from the steady-state and at high heating rates above 90 K/s transient nucleation effects become evident. This transient nucleation phenomenon is studied experimentally for the first time in the current thesis. Once supercritical nuclei are present, they begin to grow. The crystallization temperature, which depends on the heating rate, determines the crystal growth rate. At a later stage of crystallization a thermal front traverses the BMG specimen. In levitation experiments, this thermal front is taken as the solid-liquid interface and its velocity as the steady-state crystal growth rate. However, the thermal front observed during flash-annealing, propagates through the specimen about a magnitude faster than is known from solidification experiments of levitated supercooled liquids. As microstructural investigations show, crystals are present in the whole specimen, that means far ahead of the thermal front. Therefore, it does not represent the solid-liquid interface and results from the collective growth of crystals in confined volumes. This phenomenon originates from the high density of crystals and becomes evident during the heating of metallic glass. It could be only observed for the first time in the current thesis due to the high temporal resolution of the high-speed camera used.
The heating rate and temperature to which the BMG is flash-annealed determine the nucleation rate and the time for growth, respectively. The size and number of B2 CuZr crystals can be deliberately varied. Thus mechanical properties of B2 CuZr BMG composites can be studied as a function of the volume fraction and average distance of B2 particles. Cu44Zr44Al8Hf2Co2 BMG specimens were flash-annealed at a lower and higher heating rate (35 K/s and 180 K/s) to different temperatures above Tx and subsequently subjected to uniaxial compression. BMG composites prepared at higher temperatures show a lower yield strength and larger plastic strain due to the higher crystalline volume fraction. They not only exhibit plasticity in uniaxial compression, but also ductility in tension as a preliminary experiment demonstrates. Furthermore, nanocrystals precipitate in the amorphous matrix of BMG composites during deformation. They grow deformation-induced from quenched-in nuclei, which are stimulated during flash-annealing.
In essence, flash-annealing of BMGs is capable of giving insight into most fundamental scientific questions. It provides a deeper understanding of how annealing affects the structural state of metallic glasses. The number and size of structural heterogeneities can be adjusted to prepare BMGs with improved plasticity. Furthermore, crystallization kinetics of liquids can be studied as they are rapidly heated. Transient nucleation effects arise during rapid heating of BMGs and they cannot be described using the steady-state nucleation rate. Therefore, an effective nucleation rate was introduced. Besides, the flash-annealing process rises the application potential of BMGs. The microstructure of BMG composites comprised of uniformly distributed crystals and the glass, can be reliably tailored. Thus, flash-annealing constitutes a novel method to design the mechanical properties of BMG composites in a reproducible manner for the first time. BMG composites, which exhibit high strength, large plasticitiy and as in the case of B2 CuZr BMG composites as well work-hardening behaviour, can be prepared, so that the intrinsic brittleness of monolithic BMGs is effectively overcome.
|
284 |
Channel and Noise Variance Estimation for Future 5G Cellular NetworksIscar Vergara, Jorge 10 November 2016 (has links)
Future fifth generation (5G) cellular networks have to cope with the expected ten-fold increase in mobile data traffic between 2015 and 2021. To achieve this goal, new technologies are being considered, including massive multiple-input multiple-output (MIMO) systems and millimeter-wave (mmWave) communications. Massive MIMO involves the use of large antenna array sizes at the base station, while mmWave communications employ frequencies between 30 and 300 GHz. In this thesis we study the impact of these technologies on the performance of channel estimators.
Our results show that the characteristics of the propagation channel at mmWave frequencies improve the channel estimation performance in comparison with current, low frequency-based, cellular networks. Furthermore, we demonstrate the existence of an optimal angular spread of the multipath clusters, which can be used to maximize the capacity of mmWave networks. We also propose efficient noise variance estimators, which can be employed as an input to existing channel estimators.
|
285 |
The genesis of ‘giant’ copper-zinc-gold-silver volcanogenic massive sulphide deposits at Tambogrande, Perú : age, tectonic setting, paleomorphology, lithogeochemistry, and radiogenic isotopesWinter, Lawrence Stephen 11 1900 (has links)
The ‘giant’ Tambogrande volcanogenic massive sulphide (VMS) deposits within the Cretaceous Lancones basin of northwestern Perú are some of the largest Cu-Zn-Au-Ag-bearing massive sulphide deposits known. Limited research has been done on these deposits, hence the ore forming setting in which they developed and the key criteria that permitted such anomalous accumulation of base-metal sulphides are not understood.
Based on field relationships in the host volcanic rocks and U-Pb geochronology, the deposits formed during the early stages of arc development in the latest Early Cretaceous and were related to an extensional and arc-rift phase (~105-100 Ma, phase 1). During this time, bimodal, primitive basalt-dominant volcanic rocks were erupted in a relatively deep marginal basin. Phase 1 rhyolite is tholeiitic, M-type, and considered to have formed from relatively high temperature, small batch magmas. The high heat flow and extensional setting extant during the initial stages of arc development were essential components for forming a VMS hydrothermal system. The subsequent phase 2 (~99-91 Ma) volcanic sequence comprises more evolved mafic rocks and similar, but more depleted, felsic rocks erupted in a relatively shallow marine setting. Phase 2 is interpreted to represent late-stage arc volcanism during a waning extensional regime and marked the transition to contractional tectonism.
The Tambogrande deposits are particularly unusual amongst the ‘giant’ class of VMS deposits in that deposition largely occurred as seafloor mound-type and not by replacement of existing strata. Paleomorphology of the local depositional setting was defined by seafloor depressions controlled by syn-volcanic faults and rhyolitic volcanism. The depressions were the main controls on distribution and geometry of the deposits and, due to inherently confined hydrothermal venting, enhanced the efficiency of sulphide deposition.
Geochemical and radiogenic isotope data indicate that the rhyolites in the VMS deposits were high temperature partial melts of the juvenile arc crust that had inherited the isotopic signatures of continental crust. Moreover, Pb isotope data suggest the metal budget was sourced almost wholly from mafic volcanic strata. Therefore, unlike the implications of many conventional models, the felsic volcanic rocks at Tambogrande are interpreted to have only played a passive role in VMS formation. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
|
286 |
Exploring gravityBerry, Christopher P. L. January 2014 (has links)
Gravitation is the dominant influence in most astrophysical interactions. Weak-field interactions have been extensively studied, but the strong-field regime remains largely unexplored. Gravitational waves (GWs) are an excellent means of accessing strong-field regions. We investigate what we can learn about both astrophysics and gravitation from strong-field tests and, in particular, GWs; we focus upon extreme-mass-ratio (EMR) systems where a small body orbits a much more massive one. EMR bursts, a particular class of GW signals, could be used to determine the properties of massive black holes (MBHs). They could be detectable with a space-borne interferometer from many nearby galaxies, as well as the Galactic centre. Bursts could provide insightful constraints on the MBHs' parameters. These could elucidate the formation history of the MBHs and, by association, their host galaxies. The Galactic centre is the most promising source. Its event rate is determined by the stellar distribution surrounding the MBH; the rate is not high, but we still expect to gain useful astronomical information from bursts. Strong-field tests may reveal deviations from general relativity (GR). We calculate modifications that could be observed assuming metric f(R)-gravity as an effective alternative theory. Gravitational radiation is modified, as are planetary precession rates. Both give a means of testing GR. However, existing laboratory measurements already place tighter constraints on f(R)-gravity, unless there exists a screening effect, such as the chameleon mechanism, which suppresses modifications on small scales. To make precision measurements of astrophysical systems or place exacting bounds on deviations from GR, we must have accurate GW templates. Transient resonances are currently not included in the prescription for generating EMR inspiral waveforms. Their effects can be estimated from asymptotic expansions of the evolving orbital parameters. The quantitative impact on parameter estimation has yet to be calculated, but it appears that it shall be necessary to incorporate resonances when creating inspiral waveforms.
|
287 |
Etude des déformations différées des bétons en compression et en traction, du jeune au long terme : application aux enceintes de confinement / Study of delayed strains for concrete in compression and in tension from early age to long termHilaire, Adrien 28 November 2014 (has links)
Ce travail a pour but d'apporter des éléments de connaissance sur le comportement des enceintes de confinement des centrales nucléaires françaises. L'aptitude au confinement de ce type de structures est garantie par la faible perméabilité du béton. En cas d'accident, le béton est protégé de la fissuration par la compression biaxiale assurée par les câbles de précontrainte orthoradiaux et verticaux. Dès lors, il s'agit de vérifier deux points principaux : premièrement, le niveau de précontrainte doit rester suffisamment élevé pour équilibrer les contraintes de traction induites lors d'un accident, deuxièmement, la fissuration du matériau qui apparaît hors situation accidentelle doit être limitée. La réalisation de ces objectifs passe par la connaissance du comportement du béton depuis sa fabrication jusqu'à la fin de la durée d'exploitation du réacteur. L'étude du matériau est séparé en deux grandes périodes : la phase du jeune âge caractérisée par de forts couplages chemo-thermo-mécaniques et la phase du long terme où le matériau subit des sollicitations hydro-mécaniques. Une modélisation couplant l'hydratation, les transferts thermiques et hydriques et la mécanique est développée : elle est apte à décrire les principaux mécanismes en jeu. Ce modèle est implanté dans le logiciel CAST3M : le nombre limité de paramètres permet de faciliter le processus d'identification. En parallèle à ce travail de modélisation, plusieurs essais expérimentaux ont été réalisés : certains sont destinés à la détermination de paramètres spécifiques (par exemple, le coefficient de Poisson du fluage propre), d'autres ont pour but d'évaluer la pertinence des mécanismes physiques retenus dans la modélisation (notamment sur les couplages séchage-retrait-fluage). Par la diversité des phénomènes abordés, cette étude s'articule autour de plusieurs axes. La première partie traite des phénomènes thermo-chimiques du béton au jeune âge et du séchage des matériaux cimentaires : problèmes qui ont en commun leur nature diffuse. Une attention particulière est portée sur l'identification des principaux paramètres d'influence de ces deux phénomènes. La deuxième partie concerne l'étude des déformations différées du béton. Contrairement à la décomposition conventionnelle de ces déformations, fluage et retrait sont corrélés et induisent un endommagement du matériau. La modélisation proposée, qui se place dans le cadre de la mécanique des milieux poreux non saturés, permet de considérer une partie des interactions entre ces déformations. La dernière partie se concentre sur l'étude du comportement différé de structures. Les résultats mettent en lumière l'importance de certains verrous technologiques dans la prédiction du comportement à long terme d'une enceinte de confinement. / This work aims to study the behaviour of the containment buildings in a nuclear power plant. The gas-proofing of these structures is based on the low conductivity of concrete (the hydraulic conductivity is around 10-11 m/s for a standard concrete). However, if cracks appear, this material property increases and the containment may not be longer guaranteed. In accidental situations, the concrete is protected from cracking by the bi-axial prestressing of the internal safety enclosure. The ageing of the structure may have two main consequences : firstly, the prestress has to remain sufficiently high to counterbalance the tensile stress caused by an accident, secondly, cracking induced by non-accidental loads has to be limited. These aims cannot be satisfied if the behaviour of the concrete is not understood from its manufacturing to the end of the operating life of the nuclear reactor.\\ The lifespan of the structure is broken down into two distinguished periods : on one hand, strong chemo-thermo-mechanical couplings characterise the early age phase, on the other hand, the material is under hydro-mechanical stress during the long term phase. In the proposed modelling, hydration, thermal and hydric transfers are coupled with the mechanical behaviour of the concrete- the main mechanisms are considered. The model is implemented in the software \textit{CAST3M} : the limited number of parameters facilitate the identification process. In tandem with this work, several experimental tests are realised. Parameters are identified from their results, moreover, some of the experimental observations confirmed the physical mechanisms considered in the model. \\ Because of the complexity of the different phenomenon, this document is built around the following principles. The first part deals with the chemo-thermal couplings at early age and the drying process of concrete at long term : the nature of these two problems is diffusive. This part is focused on the identification of the main parameters of these two phenomenons. The second part is about the delayed strains in concrete. Unlike the conventional decomposition of these strains, creep and shrinkage are correlated and influence the damage evolution. Mechanics of unsaturated porous media is used to consider the couplings between these strains. The last part is focused on the delayed behaviour of structures. Results highlight the importance of some technological barriers in order to predict accurately the long-term behaviour of a containment building.
|
288 |
Procura de Estrelas de Alta Massa em Formação / Search for Massive Stars in Early Stages of FormationFelipe Donizeti Teston Navarete 29 October 2013 (has links)
O mecanismo de formação de estrelas de alta massa é um dos problemas fundamentais em Astrofísica e um dos menos compreendidos. Duas teorias predizem a formação destes objetos, que se formariam via i) colisão de estrelas de baixa massa, ou ii) acreção por disco circunstelar. Atualmente, ambas as teorias carecem de testes observacionais críticos. Não obstante, o número de estrelas de alta massa jovens já identificadas na Galáxia corresponde a uma fração muito menor do que o esperado pela função de massa inicial. Este trabalho apresenta um estudo observacional de candidatos a MYSOs, selecionados a partir do levantamento Red MSX Source. Observações de 376 objetos nos filtros estreitos do H2 em 2.12 mícrons e num contínuo adjacente foram realizadas para identificar jatos moleculares colimados e 296 delas são apresentadas nesse trabalho. As observações do hemisfério Norte foram realizadas com o telescópio CFHT (Havaí) enquanto os objetos do hemisfério Sul, foram observados com o telescópio SOAR (Chile). A análise dos mapas de emissão em H2 permitiu concluir que 150 dos 296 objetos (51%) estão associados a emissões extensas em H2, e 62 delas foram classificadas como emissões polares. A análise da razão de aspecto das estruturas identificadas mostra que as emissões associadas a fontes com maior luminosidade apresentam baixo grau de colimação, tal como sugere o cenário de geração dos jatos a partir de ventos emanados pela pressão de radiação do disco circunstelar. A baixa fração de emissões polares (apenas 21% da amostra) indica que o tempo de vida dessas estruturas devem ser curtos. As evidências observacionais encontradas nesse trabalho corroboram o cenário de acreção via disco circunstelar e invalidam o modelo formação via coalescência de estrelas de baixa massa, que requer ambientes relativamente densos e não é capaz de produzir jatos colimados. / Very few massive stars in early formation stages were clearly identified in our Galaxy. The formation process of these objects is still unclear and two theories predict the formation of massive stars: i) by merging of low mass stars or ii) by an accretion disk. There are no critical observational evidences to choose between them. The lack of observational evidences combined with the small number of known massive stars in formation in our Galaxy does not allow us to choose between these scenarios. We present a near-infrared survey of MYSOs candidates selected from the Red MSX Source survey. Such catalog is based on an accurate revision of distances and luminosities, overcoming the limitations and failures in previous searches of this kind. 376 targets were observed through the H2 narrow-band filter at 2.12 microns and in the continuum to identify collimated molecular jets. 296 targets were successfully processed using the THELI pipeline and are presented. Observations in the Northern Hemisphere were carried at the CFHT telescope (Hawaii) while the Southern targets were observed with the Soar Telescope (Chile). The results show that 150 of the 296 sources display extended H2 emission and 62 of them are polar. The analysis of the aspect ratio of the structures indicates that emissions associated with higher luminosity sources have low degree of collimation. This is in agreement with the scenario of the radiation pressure-driven outflows from the circunstellar discs. The low fraction of sources associated with polar jets (21%) indicates a short timescale of such structures. The observational evidences found on this work support the accretion scenario and show that coalescence of low-mass stars (which may require relatively dense environments and is not expected to produce jet-like structures) is not likely to explain most of the studied MYSOs candidates.
|
289 |
Braços espirais da galáxia: posição das regiões HII gigantes e formação estelar / Spiral Arms of the Galaxy: Position of the giant HII Regions and Star FormationAlessandro Pereira Moisés 08 April 2010 (has links)
Nesta tese é apresentado um catálogo fotométrico no infravermelho próximo de 35 Regiões HII, todas pertencentes ao disco Galáctico. Esta faixa espectral é útil uma vez que os comprimentos de onda são grandes o suficiente para se ter uma baixa extinção interestelar comparada ao visível, e são pequenos o suficiente para diagnosticar as fotosferas estelares. Foram obtidas imagens nas bandas J, H e K e imagens do Spitzer nos canais de 3,5, 5,8 e 8,0 m. Após a fotometria nas imagens JHK, foi possível construir diagramas cor-cor e cor-magnitude. Foram utilizadas imagens coloridas, compostas de uma combinação RGB das imagens nas três bandas, tanto para as imagens JHK quanto para as imagens do Spitzer. Estas imagens, junto com os diagramas, foram utilizadas para levantar candidatos a fontes ionizantes das regiões HII, assim como objetos ainda em estágios primordiais de evolução (CTTs e MYSOs). Estes dados também foram utilizados para associar à cada região HII um estágio evolutivo (de A até D, da região mais jovem à mais evoluída). Baseado na posição da Sequência Principal em diagramas cor-magnitude, foi possível comparar as distâncias cinemáticas com nossos dados. Além disso, quando possível, foram utilizadas distâncias de regiões HII determinadas por paralaxe espectrofotométrica (disponíveis na literatura) e utilizando duas leis de extinção interestelar extremas mostrou-se que estas distâncias são menores que suas contrapartidas cinemáticas, e estão em acordo com distâncias determinadas por outros métodos, como por paralaxe trigonométrica. Sabendo que estas regiões de formação estelar seguem a dinâmica do gás, o mapeamento da distribuição destas regiões permite checar a estrutura espiral da Via Láctea. / In this work, a near infrared photometric catalog of 35 HII regions that belongs to the Galactic plane is presented. This spectral range is useful since the wavelengths are long enough to have less influence of the interstellar extinction compared to the visible domain, and they are small enough to still show stellar photospheric features. Images of these HII regions in the J, H and K-band together with IRAC-Spitzer images (channels 4.5, 5.8 and 8.0 m) were used. After the photometry in the JHK images, color-color and color-magnitude diagrams were constructed. These two group of images (JHK and 4.5, 5.8 and 8.0 m) colored in a RGB combination were used, together with the diagrams, to identify the ionizing sources candidates, as well as objects still embedded in their natal cocoon (CTTs and MYSOs). An evolutionary stage to these regions (from A to D, from the younger region to the more evolved) was inferred based on the images and diagrams. These diagrams were also used to infer if the kinematic distance is correct, based on the Main Sequence location. Non-kinematic distances to several HII regions, when it was possible, were collected from the literature. Using two extreme interstellar extinction laws, it was possible to compare these distances with the kinematic results. These non-kinematic distances are lower than that from kinematic techniques. Also, these distance discrepancies are in agreement with distances derived by others methodologies, as trigonometric parallax. Since these star forming regions follow the gas dynamics, mapping their distribution along the Galaxy allows to check the spiral pattern of the Milky Way.
|
290 |
Gamification inom MOOCs : Framsteg och utmaningarFrank, Oscar January 2021 (has links)
Den här uppsatsen utforskar tidigare litteratur på gamification inom Massive Online OpenCourses (MOOCs) för att undersöka hur gamification uppfattas som ett verktyg i MOOCs.Analysverktyget som används är en kvantitativ innehållsanalys som avgränsar genomsökningentill 17 publikationer om gamification i MOOC. I korthet visar resultatet att gamification harpotential att främja undervisning i MOOCs. Majoriteten av litteraturen är positiv tillgenomförandet av gamification. Denna uppsats föreslår, baserat på resultatet, att socialinteraktion är ett mycket viktigt element för eleverna att hålla sig motiverade och elementet harblivit mer framstående i forskningen i takt med att MOOCs har vuxit och utvecklats. / This thesis explores previous literature on gamification in Massive Online Open Courses(MOOCs) to investigate how gamification is perceived as a tool in MOOCs. The analytical toolis a quantitative content analysis that narrow down to 17 publications on gamification inMOOCs. In brief, the findings show that gamification has potential to improve education inMOOCs . The majority of the literature is positive towards the implementation of gamification.This thesis suggests based on the findings that social interaction as a gamification element isvery important for learners to stay motivated and has become more noticeable the previousyears as MOOCs have grown and developed.
|
Page generated in 0.03 seconds