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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.
131

Variable Polarization from Co-Rotating Interaction Regions in Massive Star Winds

Ignace, Richard 01 January 2017 (has links)
Co-rotating Interaction Regions (CIRs) are a well-known phenomenon in the solar wind, and is a favored culprit for certain cyclical behavior observed in the spectra of some massive stars. A prime example are the discrete absorption components (DACs) seen in the UV wind lines of many O stars. Here we report on modeling for the variable continuum polarization that could arise from the presence of CIR structures. Considerations are limited to optically thin scattering. Using a core-halo approach for winds that are thick to electron scattering, an application to observed variable polarization of WR6 (EZ CMa; HD 50896) is presented.
132

Painel estrutural de madeira maciça tipo DCLT: estudo experimental, analítico e numérico de dois painéis de lamelas cruzadas com ligações cavilhadas / Massive wood structural panel type DCLT: experimental, analytical and numerical study of two panels of crossed lamellae with doweled connections

Pereira, Marcos Cesar de Moraes 13 June 2019 (has links)
O setor da construção civil em países desenvolvidos tem caminhado no sentido da industrialização e da sustentabilidade dos materiais construtivos e estruturais, e neste sentido a construção em madeira maciça tem ganhado destaque. Produtos como painéis de CLT já estão sendo usados para construção de grandes prédios multipavimentos, porem outros produtos que utilizam o mesmo princípio da laminação cruzada vem ganhando espaço, como é o caso do painel de lamelas cruzadas cavilhadas, chamado de DCLT. Neste estudo, avaliou-se o comportamento estrutural de painéis DCLT com lamelas feitas com madeira de Pinus Elliottii e Pinus Taeda e cavilhas de pau-roxo (Peltogyne spp., Leguminosae), onde foi desenvolvido um modelo de ensaio específico para as ligações neste tipo de painel, simulações em software de elementos finitos no modelo de ensaio desenvolvido, ensaios de flexão nos painéis de tamanho estrutural e posterior comparação com os métodos analíticos de cálculo de painéis de lamelas cruzada. Os resultados obtidos para rigidez dos painéis foram de 727 e 1353 kNm² para o painel de 3 e 5 camadas, respectivamente. Os valores analíticos ficaram muito próximos aos valores experimentais, validando o novo procedimento de ensaio com o qual foi obtido o valor do módulo de deslizamento usado nos cálculos analíticos. Em termos de resistência, o painel de 3 camadas se mostrou mais resistente, pois com uma dimensão menor, resistiu proporcionalmente mais carga. De maneira geral, os painéis poderiam vencer vãos de até quatro metros suportando uma carga de 150 kg/m², mostrando ser um potencial produto para uso em obras residenciais. / The construction sector in developed countries has been moving towards industrialization and sustainability of construction and structural materials and in this sense solid wood construction has gained prominence. New products such as CLT panels are used for construction of multi-storey building, and other products that use the same principle of cross lamination have been gaining ground, as is the case of the dowel cross laminated timber panel, called DCLT. In this study, we evaluated the structural behavior of DCLT panels with Pinus Elliottii and Pinus Taeda wood lamellae and pau-roxo dowels (Peltogyne spp., Leguminosae), where a specific test model was developed for connections in this type. Finite element simulations was made for the developed test model, bending tests on structural size panels and subsequent comparison with the analytical methods of calculating cross sided panels. The results obtained for the sttiffiness of the panels were 727 and 1353 kNm² for the 3 and 5 layer panels, respectively. The analytical values were very close to the experimental values, validating the new test procedure with which the value of the slip module used in the analytical calculations was obtained. In terms of strength, the 3-layer panel was more resistant, because with a smaller size, it resisted proportionally more load. In general, the panels could cover span of up to four meters supporting a load of 150 kg/m², proving to be a potential product for use in residential works.
133

Observations et modélisations de proto-étoiles massives dans le cadre de l'observatoire spatial Herschel

Marseille, M. 27 November 2008 (has links) (PDF)
La formation des étoiles massives reste, à ce jour, encore mal connue à cause de l'extrême quantité d'énergie que ces étoiles dégagent, limitant en conséquence leurs masses théoriques et contredisant les observations de ce type d'étoile. Les observatoires du futur (en particulier l'observatoire spatial Herschel) vont tenter de répondre à cette problématique grâce notamment aux émissions moléculaires de l'eau. L'analyse précise et correcte de ces données, dans l'avenir, nécessite donc dès aujourd'hui un travail associant des observations et des modélisations des objets concernés. C'est dans ce but que cette thèse a consisté en l'élaboration d'une méthode de modélisation dite « globale » d'objets proto-stellaires massifs (proto-amas ou cœurs denses massifs). Celle-ci a permis une description physique et une étude chimique des multiples cœurs denses massifs étudiées, et a ouvert de nombreuses voies vers des aspects évolutifs. Elle a également donné des indices pour affiner le programme d'observation en temps garanti WISH des raies moléculaires de l'eau et confirmé le rôle clef de cette molécule pour la compréhension de la formation des étoiles massives.
134

My World of Warcraft : en studie om de komponenter i onlinerollspelet World of Warcraft som lockar till deltagande.

Lindqvist, Anna January 2008 (has links)
Fler timmar och större intresse läggs idag ner på onlinerollspel vilka under de senaste åren blivit omåttligt populära. Våra sociala beteenden har idag förändrats och vi behöver inte längre fysiskt beträda det rum vi vanligen kommunicerade i. Vi öppnar istället upp dörrarna till en ny dimension där du “är” en virtuell identitet, och där du kanske har väldigt många fler möjligheter än i ditt fysiska liv. World of Warcraft är just ett sådant spel vilket underhåller tusentals av spelare och som kommer ligga till grund för denna uppsats. Syftet är att skapa en dokumentation av och ge en insyn i dessa nya sociala miljöer som vi finner i World of Warcraft. Vad har tillexempel en online identitet för betydelse för jaget (spelaren) och kan det som händer i ett community på internet påverka våra fysiska sociala liv? Samma sak händer om man vänder på frågan, vad händer med spelvärldens sociala liv om man inte spelar tillräckligt mycket, hur påverkar det spelandet i sig? Är en spelare tvungen att välja bara en social arena, eller finns det en god möjlighet till en balans mellan miljöerna? Frågor om interagerbarhet, interaktivitet och kommunikation i spelet kommer också att vara centrala i uppsatsen, eftersom dessa i någon form påverkar oss som individer och sociala varelser. Alltså vad är det som lockar och varför kan vi som individer bli påverkade av detta? De komponenter jag finner mest bidragande till delaktighet i World of Warcraft diskuteras och analyseras sedan utifrån utvalda teoretiska utgångspunkter. Syftet är också att utifrån videoinspelade intervjuer med spelarna ge en slags bild av hur fenomenet kan se ut. I Själva dokumentärfilmen ( som tillhör uppsatsen och som finns på separat DVD) läggs Fokus på intervjuerna, (där de intervjuade får en chans att säga sin mening) och de spelmiljöer man kan stöta på i World of Warcraft . Vi följer spelaren in i världen .Med dessa rörliga bilder kan vi också få större förståelse för vad World of Warcraft är och vad det betyder för miljontals människor. I intervjuerna med dessa respondenter försöker jag att gå in i samtal som är mer djupgående och kvalitativa. Denna form av undersökning, där så få personer medverkar kan inte kvantitativt framlägga ett övergripande mönster av hur majoritetens spelvanor ser ut.
135

Linear Precoding Performance of Massive MU-MIMO downlink System

Pakdeejit, Eakkamol January 2013 (has links)
Nowadays, multiuser Multiple-In Multiple-Out systems (MU-MIMO) are used in a new generation wireless technologies. Due to that wireless technology improvement is ongoing, the numbers of users and applications increase rapidly. Then, wireless communications need the high data rate and link reliability at the same time. Therefore, MU-MIMO improvements have to consider 1) providing the high data rate and link reliability, 2) support all users in the same time and frequency resource, and 3) using low power consumption. In practice, the interuser interference has a strong impact when more users access to the wireless link. Complicated transmission techniques such as interference cancellation should be used to maintain a given desired quality of service. Due to these problems, MU-MIMO with very large antenna arrays (known as massive MIMO) are proposed. With a massive MU-MIMO system, we mean a hundred of antennas or more serving tens of users. The channel vectors are nearly orthogonal, and then the interuser interference is reduced significantly. Therefore, the users can be served with high data rate simultaneously. In this thesis, we focus on the performance of the massive MU-MIMO downlink where the base station uses linear precoding techniques to serve many users over Rayleigh and Nakagami-m fading channels.
136

Mineralization and Alteration of the Late Triassic Glacier Creek Cu-Zn VMS Deposit, Palmer Project, Alexander Terrane, Southeast Alaska

Steeves, Nathan 14 January 2013 (has links)
The Glacier Creek volcanogenic massive sulfide (VMS) deposit is hosted within Late Triassic, oceanic back-arc or intra-arc, rift-related, bimodal volcanic rocks (Hyd or Tats Group) of the allochthonous Alexander terrane known as the Alexander Triassic Metallogenic Belt (ATMB). The deposit presently consists of four tabular massive sulfide lenses with a resource of 4.75 Mt. at 1.84% Cu, 4.57% Zn, 0.15% Pb, 0.28 g/t Au and 29.07 g/t Ag. A deposit-scale thrust fault offsets stratigraphy along the axial surface of a deposit-scale anticline. The massive sulfide lenses are barite-rich and are divided into 6 main ore-types based on mineral assemblages. There is a large range of sphalerite compositions, with low-Fe sphalerite dominant throughout the lenses and high-Fe sphalerite at the top and bottom of the lenses in pyrrhotite-rich zones. Lenses contain anomalous Sb, Hg and Tl. Gangue minerals include barite, quartz, barian-muscovite, calcite, albite, highly subordinate chlorite and locally hyalophane and celsian. Overlying massive sulfide is a tuffaceous hydrothermal sediment with anomalous REE patterns and local hyalophane. The general footwall to all four lenses is a thick unit of coherent to volcaniclastic feldspar-phyric basalt containing extensive lateral alteration. Four alteration facies are recognized based on mineral assemblages. Mass balance calculations for the footwall indicate general gains of S, Fe, Si and K with coincident loss of Ca, Na and Mg, along with trace element gains of Tl, Sb, Hg, Ba, Zn, Cu, As and loss of Sr with increased alteration intensity. Short wavelength infrared (SWIR) spectroscopy shows a general decrease in Na, K and Al content of muscovite and increase of Fe+Mg and Ba content towards ore. Integrated petrographic, mineral, chemical and sulfur-isotope data suggest a transition during deposit formation, from high-temperature, acidic, reduced hydrothermal fluids mixing with oxidized, SO4-rich seawater, to later cooler, low fO2-fS2 conditions of formation and a lack of SO4 in seawater.
137

Ni-free Ti-based Bulk Metallic Glasses: Glass Forming Ability and Mechanical Behavior

Zheng, Na 30 July 2013 (has links) (PDF)
Metallic glasses are amorphous alloys that do not possess long-range structural order in contrast to crystalline alloys. Ni-free Ti-based bulk metallic glasses (BMGs) have potential for biomedical applications due to their attractive properties such as high strength, good corrosion resistance and excellent micro-formability, which cannot be obtained for conventional crystalline alloys. In this PhD thesis, Ni-free Ti-based BMGs, i.e. Ti40Zr10Cu34Pd14Sn2 and Ti40Zr10Cu36-xPd14Inx (x = 0, 2, 4, 6, 8), were prepared in the shape of rods by suction casting. Both alloy classes were systematically characterized in terms of glass forming ability, thermal stability, phase formation and mechanical properties. The largest diameter obtained in the fully glassy state for Ti40Zr10Cu34Pd14Sn2 alloy is 3 mm and for Ti40Zr10Cu36-xPd14Inx (x = 2, 4, 6, 8) alloys is 2 mm. Base alloy (Ti40Zr10Cu36Pd14) contains some crystalline phase(s) in the glassy matrix for a 2 mm diameter rod. The structural transformations of Ti40Zr10Cu34Pd14Sn2 BMG upon heating were thoroughly analyzed by utilizing different combination of methods. Firstly, we used differential scanning calorimetry (DSC), X-Ray diffraction (XRD) and transmission electron microscopy (TEM) to investigate the first crystallization event. The main products of the first crystallization are possibly -(Ti, Zr) and Cu3Ti (orthorhombic) phases. Secondly, we employed in situ x-ray diffraction in transmission mode using synchrotron beam to deeply study the thermally-induced structural changes like relaxation, glass transition and crystallization. Since the first peak in the diffraction patterns reflects the structure of the glassy phase on the medium-range scale, the position, width and intensity of this peak in diffraction patterns are fitted through Voigt function below 800 K. All the peak position, width and intensity values show a nearly linear increase with increasing temperature to the onset temperature of structural relaxation, Tr = 510 K. However, these values start to deviate from the linear behavior between Tr and glass transition temperature Tg. The changes in the free volume, which was arrested during rapid quenching of the BMG, and the coefficient of volumetric thermal expansion prove that the aforementioned phenomenon is closely related to the structural relaxation. Above 800 K, three crystallization events are detected and the first exothermic event is due to the formation of metastable nanocrystals. For the Ti40Zr10Cu34Pd14Sn2 alloy, 2 mm diameter rods exhibit the best combination of mechanical properties (e.g. large plastic strain and high yield strength) among all the diameters (ø2, ø3 and ø4 mm) under the room-temperature compression tests. With the aim to improve its room-temperature mechanical properties, the processes of pre-annealing and cold rolling have been applied for the 2 mm diameter rods. Annealed and quenched specimens below Tg and in the supercooled liquid region (between Tg and onset crystallization temperature Tx) do not lead to the enhancement of the plasticity compared to as-cast alloys due to annihilation of excess free volume and crystallization. Cold rolling can effectively improve the plasticity of this BMG by inducing structural heterogeneities. Rolled samples up to a thickness reduction of 15% result in the largest plasticity of 5.7%. Low yield strength and visible work hardening ability are observed in the both 10%-rolled and 15%-rolled samples. The deformation behavior of Ti40Zr10Cu34Pd14Sn2 BMG at the elevated temperatures slightly below Tg and in the supercooled liquid region has been investigated. The stress-strain relations for this BMG over a broad range of temperatures (298 ~716 K) and strain rates (10-5 to 10-3 s-1) were established in uniaxial compression. Under compression tests at the highest test temperature of 716 K, the Ti-based BMG partially crystallizes and low strain rates can lead to the formation of larger volume fractions of crystals. In order to further improve the plasticity of Ti-Zr-Cu-Pd BMGs and simultaneously reduce the content of Cu (considering harmful element for the human body), the Ti40Zr10Cu36-xPd14Inx (x = 2, 4, 6, 8) BMGs have been newly developed with different short- or medium-range order in the structure. The compressive global strain of Ti40Zr10Cu36-xPd14Inx (x = 0, 2, 4, 6, 8) can be significantly improved from 4.5% for the In-free alloy to 10.2% for x = 4. However, a further increase of the indium content to 8 at.% results in a decrease of the plasticity. Among all the monolithic Ni-free Ti-based BMGs reported so far, the novel Ti40Zr10Cu32Pd14In4 BMG shows the largest plasticity. Inspired by the dislocation concept in crystalline materials, we propose a strategy for the design of ductile BMGs through minor substitution using relatively large atoms, which make the bonding nature become more metallic and with it less shear resistant. Such a locally modified structure results in topological heterogeneity, which appears to be crucial for achieving enhanced plasticity. This strategy is verified for Ti-Zr-Cu-Pd glassy alloys, in which Cu was replaced by In, and seems to be extendable to other BMG systems. The atomic-scale heterogeneity in BMGs is somewhat analog to defects in crystalline alloys and helps to improve the overall plasticity of BMGs.
138

A Tale of Two Telescopes: Taking a Closer Look at the Multiplicity Properties of Massive Stars in Cygnus

Caballero, Saida M 13 August 2012 (has links)
Massive stars profoundly influence the evolution of the Universe, from Galactic dynamics and structure to star formation. They are often found with bound companions. However, our knowledge of O-type multiple systems with periods in the range from years to thousands of years is incomplete due their great distances. We present results from a high angular resolution survey to find angularly resolved companions using the Fine Guidance Sensor (FGS) on the Hubble Space Telescope and using ground-based adaptive optics at Gemini North. We observed 75 O- and early B-type stars in Cyg OB2 and determined that 42% of the sample have at least one companion that meets a statistical criterion for gravitationally bound status. As a case study, we present an examination of high resolution, ultraviolet spectroscopy from Hubble Space Telescope of the photospheric spectrum of the O-supergiant in the massive X-ray binary HDE 226868 = Cyg X-1. We analyzed the ultraviolet and ground-based optical spectra to determine the effective temperature and gravity of the O9.7 Iab supergiant. Using non-LTE, line blanketed, plane parallel models from the TLUSTY grid, we obtain Teff = 28.0 +/- 2.5 kK and log g > 3.00 +/- 0.25, both lower than found in previous studies. The optical spectrum is best fit with models that have enriched He and N abundances. We fit the model spectral energy distribution for this temperature and gravity to the UV, optical, and IR fluxes to determine the angular size of and extinction towards the binary. By assuming that the supergiant rotates synchronously with the orbit, we can use the radius - distance relation to find mass estimates for both components as a function of the distance and the ratio of stellar to Roche radius. Our results indicate masses of 23+8-6 solarmasses for the supergiant and 11+5-3 solarmasses for the black hole. These results agree with subsequent mass estimates Orosz et al. (2011) based on the trigonometric parallax distance measurements of Reid et al. (2011). The results of this survey provide fundamental information on the impact of environment on massive binaries and also the role multiplicity has on massive star formation and evolution.
139

VALUE STREAM MAPPING – A CASE STUDY OF CONSTRUCTION SUPPLY CHAINOF PREFABRICATED MASSIVE TIMBER FLOOR ELEMENT

Marzec, Cindy, Gustavsson, Joachim January 2007 (has links)
The purpose of this Master Thesis is to study how the value stream mapping concept can be applied along the construction supply chain for prefabricated massive timber floor elements. Identification and qualification of waste are starting points to propose suggestions on how to reduce and/or eliminate them. In order to use the value stream mapping along the construction supply chain, pertinent data has been collected and analyzed. To conduct the value stream mapping, the first three steps of the lean thinking principles in construction have been followed. The first step aims at defining the customer and his value as well as the value for the delivery team and how it is specified in the product. The second step is based on identifying the value stream and this is done through defining the resources and activities needed to manufacture, deliver and install the floor elements. This is conducted by using the VSMM methodology. In addition the current practice should be standardized and key component suppliers should be defined and located. The third and last step identifies non-value adding activities, in other words waste and suggestions on how to remove and/or reduce waste have been reached. Wastes from product defects, transportation waste and waste of waiting were to be found in the construction supply chain. Propositions to reduce and/or eliminate wastes were to implement a more careful planning of the manufacturing process and production schedule, to apply lean production principles in the manufacturing facility and decrease and or eliminate storage time. The study made has shown that in the supply chain of massive timber floor elements at Limnologen there is a big potential to lower costs and increase customer value as value added-time accounted for only 2% of the total time.
140

Nano-Domain Analysis Via Massive Cluster Secondary Ion Mass Spectrometry in the Event-by-Event Mode

Pinnick, Veronica Tiffany 2009 December 1900 (has links)
Secondary ion mass spectrometry (SIMS) is a surface analysis technique which characterizes species sputtered by an energetic particle beam. Bombardment with cluster projectiles offers the following notable advantages over bombardment with atomic ions or small clusters: enhanced emission of molecular ions, low damage cross-section, and reduced molecular fragmentation. Additionally, in the case of Au4004 and C60 impacts, desorption originates from nanometric volumes. These features make clusters useful probes to obtain molecular information from both nano-objects and nano-domains. The "event-by-event bombardment/detection mode" probes nano-objects one-at-a-time, while collecting and storing the corresponding secondary ion (SI) information. Presented here are the first experiments where free-standing nano-objects were bombarded with keV projectiles of atomic to nanoparticle size. The objects are aluminum nano-whiskers, 2 nm in diameter and ~250 nm in length. Au4004 has a diameter of ~2 nm, comparable to the nominal diameter of the nanowhiskers. There are notable differences in the SI response from sample volumes too small for full projectile energy deposition. The whisker spectra are dominated by small clusters?the most abundant species being AlO- and AlO2-. Bulk samples have larger yields for AlO2- than for AlO-, while this trend is reversed in whisker samples. Bulk samples give similar abundances of large SI clusters, while whisker samples give an order of magnitude lower yield of these SIs. Effective yields were calculated in order to determine quantitative differences between the nano-objects and bulk samples. The characterization of individual nano-objects from a mixture is demonstrated with negatively charged polymer spheres that are attracted to and retained by the nano-whiskers. The spheres are monodisperse polystyrene nanoparticles (30nm diameter). Our results show that the event-by-event mode can provide information on the nature, size, relative location, and abundance of nano-objects in the field of view. This study presents the first evidence of quantitative molecular information originating from nano-object mixtures. Biologically relevant systems (solid-supported lipid bilayers) were also characterized using Au5 , Au4004 and C60 . Organization-dependent SI emission was observed for phosphocholine bilayers. Lipid domain formation was also investigated in bilayers formed from cholesterol and a mixed lipid system. Trends in the correlation coefficient suggest that cholesterol segregates from the surrounding lipid environment during raft formation.

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