1,756 research outputs found
The Multi-Object, Fiber-Fed Spectrographs for SDSS and the Baryon Oscillation Spectroscopic Survey
We present the design and performance of the multi-object fiber spectrographs
for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon
Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999
on the 2.5-m aperture Sloan Telescope at Apache Point Observatory, the
spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II
surveys, enabling a wide variety of Galactic and extra-galactic science
including the first observation of baryon acoustic oscillations in 2005. The
spectrographs were upgraded in 2009 and are currently in use for BOSS, the
flagship survey of the third-generation SDSS-III project. BOSS will measure
redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyman-alpha
absorption of 160,000 high redshift quasars over 10,000 square degrees of sky,
making percent level measurements of the absolute cosmic distance scale of the
Universe and placing tight constraints on the equation of state of dark energy.
The twin multi-object fiber spectrographs utilize a simple optical layout
with reflective collimators, gratings, all-refractive cameras, and
state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in
two channels over a bandpass covering the near ultraviolet to the near
infrared, with a resolving power R = \lambda/FWHM ~ 2000. Building on proven
heritage, the spectrographs were upgraded for BOSS with volume-phase
holographic gratings and modern CCD detectors, improving the peak throughput by
nearly a factor of two, extending the bandpass to cover 360 < \lambda < 1000
nm, and increasing the number of fibers from 640 to 1000 per exposure. In this
paper we describe the original SDSS spectrograph design and the upgrades
implemented for BOSS, and document the predicted and measured performances.Comment: 43 pages, 42 figures, revised according to referee report and
accepted by AJ. Provides background for the instrument responsible for SDSS
and BOSS spectra. 4th in a series of survey technical papers released in
Summer 2012, including arXiv:1207.7137 (DR9), arXiv:1207.7326 (Spectral
Classification), and arXiv:1208.0022 (BOSS Overview
Application of X-ray Grating Interferometry to Polymer/Flame Retardant Blends in Additive Manufacturing
X-ray grating interferometry is a nondestructive tool for visualizing the internal structures of samples. Image contrast can be generated from the absorption of X-rays, the change in phase of the beam and small-angle X-ray scattering (dark-field). The attenuation and differential phase data obtained complement each other to give the internal composition of a material and large-scale structural information. The dark-field signal reveals sub-pixel structural detail usually invisible to the attenuation and phase probe, with the potential to highlight size distribution detail in a fashion faster than conventional small-angle scattering techniques. This work applies X-ray grating interferometry to the study of additively manufactured polymeric objects. Additively manufactured bunnies made from single materialâacrylonitrile butadiene styrene (ABS) and polylactic acid (PLA)âwere studied by grating-based X-ray interferometric two-dimensional imaging and tomography. The dark-field images detected poor adhesion in the plane perpendicular to the build plate. Curvature analysis of the sample perimeter revealed a slightly higher propensity to errors in regions of higher curvature. Incorporation of flame-retardant molecules to near-surface regions of otherwise flammable objects through the fused deposition modeling additive manufacturing technique was also explored. The anticipated advantage was efficient use of the flame retardants while keeping them away from the surface for safety. To determine heat propagation effects, two-dimensional grating-based interferometry imaging at LSU CAMD was used to study heated samples. The focus was on the dark-field signals to highlight voids and gaps arising from layer delamination or gasification of chemical components. The resulting differential phase and dark-field x images were tainted by fringes attributed to inaccuracies in the grating-step position. Attempts to correct this will be presented. Interferometric tomography was also carried out on the heated samples using the W. M. Keck interferometric system at LSU. Grating-based interferometry was also used to probe scattering structure sizes of heated samples. Comparison of the data with the conventional small-angle x-ray scattering technique, SAXS, is being pursued. The results obtained so far from the above-mentioned experimental works are presented in this document
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ćș泶性ćŠ(Hiroshima University)ć棫(ć·„ćŠ)Doctor of Engineeringdoctora
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Combined Neutron Imaging and Diffraction: Instrumentation and Experimentation
A combined neutron imaging and diffraction facility, IMAT (Imaging and Materials Science & Engineering) is developed at ISIS (Target Station 2).
One subject of this thesis was focused on the design and optimization of the imaging part of IMAT, using the Monte Carlo calculation software package McStas. Hence, the neutron guide dimensions, the effects of the gaps in the neutron guide on imaging detectors, gravitation effects in the neutron guide and also the influence of the pinhole size on the image were studied. All these investigations were made taking into account the most important design criteria: to maximise the neutron flux, to obtain a good energy resolution whilst retaining a large neutron bandwidth and a long flight path and to minimize the artefacts obtained in the neutron radiographies.
After a compromise between imaging, diffraction and engineering requirements had been reached, the results from simulations specific to the current IMAT design were studied: wavelength distribution, beam profiles at different points along the beamline, beam divergence, neutron intensity distribution and flux depending on the pinhole size and the wavelength bands. Moreover, generation of IMAT imaging data with a sample led to full tomographic simulations and modelling wavelength effects.
Another objective of the thesis was to study the complementarity between neutron imaging and neutron diffraction experiments. For this, a new instrument control concept that exploits tomography data to guide diffraction experiments on samples with complex structures and shapes named âtomography driven diffractionâ (henceforth, TDD) was developed. The method has been proved to be viable using combinations of individual tomography and diffraction instruments: NEUTRA (PSI) and ENGIN-X (ISIS) for different samples drawn from the engineering and heritage sciences. On IMAT it will be possible to perform tomography, mark the measurement points and proceed to the diffraction measurements as one continuous process
Coherent methods in the X-ray sciences
X-ray sources are developing rapidly and their coherent output is growing
extremely rapidly. The increased coherent flux from modern X-ray sources is
being matched with an associated rapid development in experimental methods.
This article reviews the literature describing the ideas that utilise the
increased brilliance from modern X-ray sources. It explores how ideas in
coherent X-ray science are leading to developments in other areas, and vice
versa. The article describes measurements of coherence properties and uses this
discussion as a base from which to describe partially-coherent diffraction and
X-ray phase contrast imaging, with its applications in materials science,
engineering and medicine. Coherent diffraction imaging methods are reviewed
along with associated experiments in materials science. Proposals for
experiments to be performed with the new X-ray free-electron-lasers are briefly
discussed. The literature on X-ray photon correlation spectroscopy is described
and the features it has in common with other coherent X-ray methods are
identified. Many of the ideas used in the coherent X-ray literature have their
origins in the optical and electron communities and these connections are
explored. A review of the areas in which ideas from coherent X-ray methods are
contributing to methods for the neutron, electron and optical communities is
presented.Comment: A review articel accepted by Advances in Physics. 158 pages, 29
figures, 3 table
Star Formation Histories of Nearby Elliptical Galaxies: I. Volume Limited Sample
This work presents high spectroscopic observations of a representative
sample of nearby elliptical galaxies. These observations provide a strong test
of models for the formation of elliptical galaxies and their star formation
histories. Combining these data with the Gonzalez (1993) data set, a volume
limited sample of 45 galaxies has been defined. Results are in agreement with
previous studies: the existence of the metallicity hyper-plane and the Z-plane
of Trager et al. (2000) is confirmed, and the distribution is clearly due to
physical variations in stellar population parameters and not measurement
uncertainty. Trends between stellar population parameters and galaxy structural
parameters suggest that angular momentum may determine the chemical abundance
of a galaxy at a given mass.Comment: 11 pages, 6 tables, 21 figures, accepted for publication in A
3D approximation of scapula bone shape from 2D X-ray images using landmark-constrained statistical shape model fitting
Two-dimensional X-ray imaging is the dominant imaging modality in low-resource countries despite the existence of three-dimensional (3D) imaging modalities. This is because fewer hospitals in low-resource countries can afford the 3D imaging systems as their acquisition and operation costs are higher. However, 3D images are desirable in a range of clinical applications, for example surgical planning. The aim of this research was to develop a tool for 3D approximation of scapula bone from 2D X-ray images using landmark-constrained statistical shape model fitting. First, X-ray stereophotogrammetry was used to reconstruct the 3D coordinates of points located on 2D X-ray images of the scapula, acquired from two perspectives. A suitable calibration frame was used to map the image coordinates to their corresponding 3D realworld coordinates. The 3D point localization yielded average errors of (0.14, 0.07, 0.04) mm in the X, Y and Z coordinates respectively, and an absolute reconstruction error of 0.19 mm. The second phase assessed the reproducibility of the scapula landmarks reported by Ohl et al. (2010) and Borotikar et al. (2015). Only three (the inferior angle, acromion and the coracoid process) of the eight reproducible landmarks considered were selected as these were identifiable from the two different perspectives required for X-ray stereophotogrammetry in this project. For the last phase, an approximation of a scapula was produced with the aid of a statistical shape model (SSM) built from a training dataset of 84 CT scapulae. This involved constraining an SSM to the 3D reconstructed coordinates of the selected reproducible landmarks from 2D X-ray images. Comparison of the approximate model with a CT-derived ground truth 3D segmented volume resulted in surface-to-surface average distances of 4.28 mm and 3.20 mm, using three and sixteen landmarks respectively. Hence, increasing the number of landmarks produces a posterior model that makes better predictions of patientspecific reconstructions. An average Euclidean distance of 1.35 mm was obtained between the three selected landmarks on the approximation and the corresponding landmarks on the CT image. Conversely, a Euclidean distance of 5.99 mm was obtained between the three selected landmarks on the original SSM and corresponding landmarks on the CT image. The Euclidean distances confirm that a posterior model moves closer to the CT image, hence it reduces the search space for a more exact patient-specific 3D reconstruction by other fitting algorithms
3D Quantification of Particle Interaction of Compacted Powders Using Synchrotron Micro Tomography (SMT)
Synchrotron Micro Tomography (SMT) is a powerful, non-destructive scanning technique for studying the internal structure of materials. SMT was utilized for two applications in this thesis. The first application involves tracking particle rotation of aluminum powder under different compaction strains. The experiments were conducted on two geometrical configurations by applying axial load to compact the powder in the die and acquiring SMT scans at different strain levels. The SMT scans were processed using AVIZO visualization software for further analyses. The analyses included tracking the same particle at different compaction strain levels, analyzing their volume compressibility, and then quantifying their rotational behavior with respect to the z-axis and xy plane. Particles were first tracked, colored, and then 3D volume was generated. The main findings of this analysis include: 1) the volumetric strain of the particles decreased at high compaction strain due to breakage of the particles into small fragments and elastic volumetric strain of aluminum powder; 2) initially, particles showed no rotation, followed by significant rotation, due to an increase of compaction strains; 3) the majority of the particles exhibited significant rotations near the loading plate and the curved boundary; 4) the 3D shape of the tracked particles under different compaction strains provided a significant contribution to the research area of powders by demonstrating that particles change their shape during the application of compaction. SMT was utilized to quantify sand particles position during a Cone Penetration Test (CPT) as a second application. CPT is a fast and reliable in situ method for characterizing soil properties. A CPT was conducted on a sand specimen and the scans were acquired at different penetration depths using SMT. AVIZO was used to analyze the SMT scans with an objective of identifying how the particles change their position under different penetration depths. Individual particles were tracked and colored to perform this analysis. The results of the analyses include: 1) most particles near the top of the specimen moved upward during initial penetration, due to a small overburden pressure; 2) particles belonging to the middle and bottom of the specimen showed a downward movement with CPT advancement; 3) the tracked particles provided an insight into particle interaction with advancing cone penetration
Imagerie nanométrique 2D et 3D ultrarapide par diffraction cohérente
Coherent diffraction is an amazing art by its experimental simplicity: a coherent XUV source illuminates a single, isolated sample, and the diffraction pattern of the object is recorded by a CCD camera. An inversion of the diffraction pattern to an image in real space is possible through an approach based on iterative algorithms. The techniques for Fourier transform holography, for which reference is placed near the object to be imaged, allow the direct reconstruction of the image, even when the quality of the experimental data is worse. We have a laboratory sufficiently intense compact XUV source for this type of experience. The ultrashort XUV pulses (from femtosecond to attosecond) are produced by selecting high order harmonics of a femtosecond infrared laser which is focused into a cell of rare gas. We recently demonstrated the feasibility of using this source for coherent diffraction imaging with a spatial resolution of 78 nm. Furthermore, we demonstrated experimentally a holographic technique with extended reference and obtained a resolution of 110 nm in single shot (i.e. an integration time of 20 femtoseconds). A perception of an object in three dimensions gives us a better understanding thereof. A nanoscale 3D imaging techniques are from tomographic techniques of electron microscopy. However, many shots required (from different angles) make these techniques obsolete during the study time-resolved irreversible phenomena on non-reproducible samples. In this context, the aim of my thesis is to extend the 2D imaging techniques for 3D perception of nanoscale (physical, biological ) objects, while preserving the ultrafast appearance. The development of a new technology of 3D coherent imaging in single view, named âankylographyâ, proposed by Professor Miao J. UCLA [Raines et al., Nature 2010] was made in progress. This technique allows reconstructing a 3D image of the sample after a single diffraction image. Its basic principle is to find the depth of a 3D object by the longitudinal constructive interference. However, this technique is more requested in both the quality of experimental data and the computer hardware and analysis. The other idea for 3D imaging is to imitate human vision using two coherent beams X arriving simultaneously on the sample but with a small angle. In this scheme, we use references near the target object (i.e. holography) to improve the signal to noise ratio in the diffraction pattern (hologram). Two holograms are then collected on the same detector. The inverse Fourier of each hologram forms two images from different views of the object. Parallax is thus produced. The stereo reconstruction of the object is performed by computer. Finally, the demonstration of applications will be considered after my thesis. This imaging of biological objects (such as nanoplanktons already collected and prepared CEA). And we are also interested in the study of 3D nanoscale objects (azo-polymers) movement on ultrashort time. Furthermore, another important application will be to study the ultra-fast phase transition such as nano-magnetic field where demagnetization phenomena induced by femtosecond pulse occurs.La diffraction cohĂ©rente est une technique Ă©tonnante par sa simplicitĂ© expĂ©rimentale : une source XUV cohĂ©rente illumine un Ă©chantillon unique, isolĂ©, et la figure de diffraction de lâobjet est enregistrĂ©e sur une camĂ©ra CCD. Une inversion de la figure de diffraction Ă une image dans lâespace rĂ©el est possible grĂące Ă une approche basĂ©e sur des algorithmes itĂ©ratifs. Les techniques dâholographie par transformĂ©e de Fourier, pour lesquelles une rĂ©fĂ©rence est placĂ©e Ă proximitĂ© de lâobjet que lâon veut imager, permettent-elles la reconstruction directe de lâimage, mĂȘme lorsque la qualitĂ© des donnĂ©es expĂ©rimentales est moindre. Nous disposons dans notre laboratoire dâune source compacte XUV suffisamment intense pour rĂ©aliser ce type dâexpĂ©rience. Les impulsions XUV ultrabrĂšves (femtoseconde Ă attoseconde) sont produites en sĂ©lectionnant les harmoniques dâordre Ă©levĂ© dâun laser infra-rouge femtoseconde focalisĂ© dans une cellule de gaz rare. Nous avons rĂ©cemment dĂ©montrĂ© la possibilitĂ© dâutiliser cette source pour lâimagerie par diffraction cohĂ©rente avec une rĂ©solution spatiale de 78 nm. De plus, nous avons dĂ©montrĂ© expĂ©rimentalement une technique dâholographie avec rĂ©fĂ©rence Ă©tendue, et obtenu une rĂ©solution de 110 nm en simple tir (soit un temps dâintĂ©gration de 20 femtosecondes). Une perception dâun objet en trois dimensions nous donne une meilleure comprĂ©hension de celui-ci. A lâĂ©chelle nanomĂ©trique, les techniques dâimagerie 3D sont issues de techniques tomographiques autour de la microscopie Ă©lectronique. Cependant, les nombreuses prises de vue nĂ©cessaires (sous des angles diffĂ©rents) rendent ces techniques caduques lors de lâĂ©tude rĂ©solue en temps de phĂ©nomĂšnes irrĂ©versibles sur des Ă©chantillons non reproductibles. Dans ce contexte, le but de ma thĂšse est dâĂ©tendre les techniques dâimagerie 2D Ă une perception 3D dâobjets nanomĂ©triques (physiques, biologiques), tout en prĂ©servant lâaspect ultrarapide. Le dĂ©veloppement dâune nouvelle technique dâimagerie cohĂ©rent 3D en seul vue, lâankylographie, proposĂ©e par le professeur J. Miao de UCLA [Raines et al., Nature 2010] a Ă©tĂ© effectuĂ©. Cette technique permet de reconstruire lâimage 3D dâun Ă©chantillon dâaprĂšs une unique image de diffraction. Son principe basique est de retrouver la profondeur dâun objet 3D par lâinterfĂ©rence constructive longitudinale. Cependant, cette technique dâimagerie cohĂ©rent 3D est plus exigeante en termes de qualitĂ© de donnĂ©es expĂ©rimentales comme en moyen informatique dâanalyse et dâinversion. Lâautre idĂ©e en imagerie 3D est de mimer la vision humaine en utilisant deux faisceaux X cohĂ©rents arrivant simultanĂ©ment sur lâĂ©chantillon mais avec un petit angle. Dans ce schĂ©ma, on utilise des rĂ©fĂ©rences Ă cotĂ© de lâobjet mire (holographie) pour amĂ©liorer le rapport signal sur bruit dans la figure de diffraction (soit hologramme). On recueille ensuite deux hologrammes sur le mĂȘme dĂ©tecteur. Lâinversion Fourier de chacun des hologrammes forme deux images issues dâune vision diffĂ©rente de lâobjet. La parallaxe est ainsi rĂ©alisĂ©e. La reconstruction stĂ©rĂ©o de lâobjet est effectuĂ©e numĂ©riquement. Enfin, des applications de dĂ©monstration seront envisagĂ©es aprĂšs ma thĂšse. Il sâagit dâimager des objets biologiques (nanoplanktons dĂ©jĂ collectĂ©s et prĂ©parĂ©s au CEA). Et nous nous intĂ©resserons Ă©galement Ă lâĂ©tude du mouvement 3D dâobjets nanomĂ©triques (azo-polymĂšres) sur des temps ultracourts. Une autre application importante sera dâĂ©tudier la transition de phase ultra-rapide tel que le nano-domaine magnĂ©tique oĂč des phĂ©nomnes de dĂ©saimantation induite par des impulsion femtoseconde ont lieu
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