2,183 research outputs found
In vitro synchrotron-based radiography of micro-gap formation at the implant–abutment interface of two-piece dental implants
Micro-radiography using hard X-ray synchrotron radiation is the first potential tool to allow an evaluation of the mechanical behavior of the dental implant–abutment complex during force application, thus enabling the enhancement of the design of dental implants which has been based on theoretical analysis to date
Reflection on multilayer mirrors beam profile and coherence properties
The main advantage of Bragg reflection from a multilayer mirror as a monochromator for hard X rays, is the higher photon flux density because of the larger spectral bandpass compared with crystal lattice reflection. The main disadvantage lies in the strong modulations of the reflected beam profile. This is a major issue for micro imaging applications, where multilayer based monochromators are frequently employed to deliver high photon flux density. A subject of particular interest is the origin of the beam profile modifications, namely the irregular stripe patterns, induced by the reflection on a multilayer. For multilayer coatings in general it is known that the substrate and its surface quality significantly influence the performance of mirrors, as the coating reproduces to a certain degree the roughness and shape of the substrate. This proceedings article reviews recent experiments that indicate potential options for producing wave front preserving multilayer mirrors, as well as new details on the particular mirrors our group has extensively studied in the pas
Híbridos e variedades de milho submetidos à inoculação de sementes com Herbaspirillum seropedicae.
Resumo: A fixação biológica de nitrogênio proporcionada por bactérias diazotróficas pode representar alternativa para a produção de milho em sistemas agrícolas mais sustentáveis ou de baixa utilização de insumos. Objetivando-se avaliar o crescimento, teor e acúmulo de nitrogênio em genótipos de milho, em função da inoculação das sementes com Herbaspirillum seropedicae, foi conduzido experimento em casa de vegetação avaliando-se 35 genótipos de milho híbridos simples, duplo, triplo e variedades. Para inoculação das sementes foi utilizado inoculante turfoso contendo a estirpe bacteriana de H. seropedicae (ZAE 94). Entre os genótipos comerciais de milho estudados, apenas nove híbridos apresentam ganhos de crescimento ou acúmulo de N com a inoculação das sementes com a estirpe Herbaspirillum seropedicae (ZAE 94). Há distinção de resposta entre cultivares de milho em termos de produção de biomassa e incremento de teor de N na parte aérea das plantas. Abstract: The biological nitrogen fixation provided by diazotrophic bacteria may represent an alternative to maize production in more sustainable agricultural systems or low use of technology. In order to evaluate the growth, content and accumulation of nitrogen in corn genotypes, depending on seed inoculation with Herbaspirillum seropedicae experiment was conducted in greenhouse evaluating 35 corn genotypes hybrid single, double, triple and varieties. For seed inoculation was used peat inoculant containing the bacterial strain of H. seropedicae (ZAE 94). Among the commercial corn genotypes studied, only nine hybrids show increase of growth or accumulation of N with the seed inoculation with Herbaspirillum seropedicae (ZAE 94). There is a distinction in response between maize cultivars in terms of biomass production and increase of N content in the shoots
Ghost Tomography
Ghost tomography using single-pixel detection extends the emerging field of
ghost imaging to three dimensions, with the use of penetrating radiation. In
this work, a series of spatially random x-ray intensity patterns is used to
illuminate a specimen in various tomographic angular orientations with only the
total transmitted intensity being recorded by a single-pixel camera (or bucket
detector). The set of zero-dimensional intensity readings, combined with
knowledge of the corresponding two-dimensional illuminating patterns and
specimen orientations, is sufficient for three-dimensional reconstruction of
the specimen. The experimental demonstration of ghost tomography is presented
here using synchrotron hard x-rays. This result expands the scope of ghost
imaging to encompass volumetric imaging (i.e., tomography), of optically opaque
objects using penetrating radiation. For hard x-rays, ghost tomography has the
potential to decouple image quality from dose rate as well as image resolution
from detector performance
Derivation of Del180 from sediment core log data\u27 Implications for millennial-scale climate change in the Labrador Sea
Sediment core logs from six sediment cores in the Labrador Sea show millennial-scale climate variability during the last glacial by recording all Heinrich events and several major Dansgaard-Oeschger cycles. The same millennial-scale climate change is documented for surface water δ18O records of Neogloboquadrina pachyderma (left coiled); hence the surface water δ18O record can be derived from sediment core logging by means of multiple linear regression, providing a paleoclimate proxy record at very high temporal resolution (70 years). For the Labrador Sea, sediment core logs contain important information about deepwater current velocities and also reflect the variable input of ice-rafted debris from different sources as inferred from grain-size analysis, the relation of density and P wave velocity, and magnetic susceptibility. For the last glacial, faster deepwater currents, which correspond to highs in sediment physical properties, occurred during iceberg discharge and lasted from several centuries to a few millennia. Those enhanced currents might have contributed to increased production of intermediate waters during times of reduced production of North Atlantic Deep Water. Hudson Strait might have acted as a major supplier of detrital carbonate only during lowered sea level (greater ice extent). During coldest atmospheric temperatures over Greenland, deepwater currents increased during iceberg discharge in the Labrador Sea, then surface water freshened shortly thereafter, while the abrupt atmospheric temperature rise happened after a larger time lag of ≥ 1 kyr. The correlation implies a strong link and common forcing for atmosphere, sea surface, and deep water during the last glacial at millennial timescales but decoupling at orbital timescales
Boosting spatial resolution by incorporating periodic boundary conditions into single-distance hard-x-ray phase retrieval
A simple coherent-imaging method due to Paganin et al. is widely employed for
phase-amplitude reconstruction of samples using a single paraxial x-ray
propagation-based phase-contrast image. The method assumes that the
sample-to-detector distance is sufficiently small for the associated Fresnel
number to be large compared to unity. The algorithm is particularly effective
when employed in a tomographic setting, using a single propagation-based
phase-contrast image for each projection. Here we develop a simple extension of
the method, which improves the reconstructed contrast of very fine sample
features. This provides first-principles motivation for boosting fine spatial
detail associated with high Fourier frequencies, relative to the original
method, and was inspired by several recent works employing empirically-obtained
Fourier filters to a similar end
Microporosity in aluminium foams
We studied microporosity in the metallic matrix of aluminium foams produced by the powder metallurgical route both with and without application of a blowing agent. Microporosity was studied in situ in liquid metal foams as well as ex situ in the solidified microstructures. In situ studies were carried out using synchrotron X rays. Quantitative analyses of the amount and distribution of microporosity inside cell walls, Plateau borders and nodes were performed on 2D micrographs and on 3D reconstructed volumes generated by X ray tomography. We studied the influence of alloying elements, blowing agent and holding time on the amount and type of micropores. The mechanisms of microporosity formation and the evolution of microporosity via diffusion of hydrogen and by coalescence are discussed. It was observed that alloy composition and holding time have a strong influence on microporosity. Different possible strategies to control microporosity are suggeste
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