| 1. |
- Blanton, Michael R., et al.
(författare)
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Sloan Digital Sky Survey IV : Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
- 2017
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Ingår i: Astronomical Journal. - : IOP Publishing Ltd. - 0004-6256 .- 1538-3881. ; 154:1
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Tidskriftsartikel (refereegranskat)abstract
- We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and. high signal-to-noise ratios in the near-infrared. The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is obtaining spatially resolved spectroscopy for thousands of nearby galaxies (median z similar to 0.03). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is mapping the galaxy, quasar, and neutral gas distributions between z similar to 0.6 and 3.5 to constrain cosmology using baryon acoustic oscillations, redshift space distortions, and the shape of the power spectrum. Within eBOSS, we are conducting two major subprograms: the SPectroscopic IDentification of eROSITA Sources (SPIDERS), investigating X-ray AGNs. and galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey (TDSS), obtaining spectra of variable sources. All programs use the 2.5 m Sloan Foundation Telescope at the. Apache Point Observatory; observations there began in Summer 2014. APOGEE-2 also operates a second near-infrared spectrograph at the 2.5 m du Pont Telescope at Las Campanas Observatory, with observations beginning in early 2017. Observations at both facilities are scheduled to continue through 2020. In keeping with previous SDSS policy, SDSS-IV provides regularly scheduled public data releases; the first one, Data Release 13, was made available in 2016 July.
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| 2. |
- Barrat, Jean-Louis, et al.
(författare)
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Soft matter roadmap
- 2024
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 2515-7639. ; 7:1
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Forskningsöversikt (refereegranskat)abstract
- Soft materials are usually defined as materials made of mesoscopic entities, often self-organised, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterise them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g. tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This Roadmap intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterisation, instrumental, simulation and theoretical methods as well as general concepts.
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| 3. |
- Safdar, Adnan, et al.
(författare)
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Effect of EBM processing parameters on surface roughness and microstructure of Ti-6Al-4V
- 2009
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Ingår i: Proceeding 22nd European Conference for Biomaterials. - : European Society for Biomaterials.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Titanium and its alloys especially Ti-6Al-4V is an attractive biomaterial due to their excellent biocompatibility. Electron Beam Melting (EBM) is one of the Solid Free Form Fabrication (SFFF) methods to build 3D solid and near-net shape objects for medical implants and aerospace industry. EBM system utilizes a high energy electron beam to selectively melt a powder layer according to CAD file in a vacuum chamber. EBM system can manufacture complex 3D geometries requiring no or very little machining before use. The EBM systems are energy and material efficient. The microstructures and surface properties of objects produced by EBM can be influenced by the setting of different processing parameters in the EBM system. In this study solid slabs of Ti-6Al-4V, approximately 5 x 5 cm with various thicknesses were produced with different sets of processing parameters such as beam current, offset focus, scan speed and scan direction. The effects of these parameters on surface roughness, surface morphology and microstructure of slabs have been evaluated by using confocal microscopy, SEM /EDX and optical microscopy. The samples for optical microscopy and SEM were prepared by using standard metallographic methods. Microstructures of Ti-6Al-4V alloy produced by EBM usually consist of columnar grains as shown in Figure 1. These grains always grow parallel to build direction. Layers of different contrasts were observed in the samples where the layer interface is perpendicular to the build direction as shown in figure 2. The growth of columnar grains and appearance of layers with different contrasts were observed irrespective of the parameter values. These two observed phenomena can be attributed to the partial reheating / re-melting of the solidified layer by the electron beam during the melting of subsequent layer. The diameter of individual grain and density of grains are not uniform and usually decreases with increase in build height. Upon cooling from the β-transus temperature, more or less continuous α-layers were found to form along the prior β grain boundaries. In the EBM produced Ti-6Al-4V alloy the β -phase was found to be in rod-like geometry, with a size of 0.05-0.1μm in diameter, imbedded in the α-plates. It was observed that the high value of off set focus can cause porosity in the sample. For example the resultant porosity could be up to 11%. On the other hand where the value of offset focus is relatively small no such phenomenon was observed. Reconstruction of 3D surface topography and roughness coefficient (Ra) were computed by using images taken from confocal microscope and novel computer program “COMSTAT’’ [A.Heydorn et al (2000)]. Figure 3 shows a 3D reconstructed surface of the EBM produced sample. The Ra is computed by using the equation below: Where Lfi is the thickness of ith point, Lf is the mean thickness and N is the number of measurements. It has been observed that the value of Ra is processing parameters dependent. A sample with bigger thickness or higher current values tends to have relatively higher values of Ra. The scan speed and scan direction can also influence the surface morphology and microstructures of the EBM produced alloys.
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