518 research outputs found
Evaluation of a compact multi-contrast and multi-resolution X-ray phase contrast edge illumination system for small animal imaging
PURPOSE: In this work the performance of a compact multi-resolution and multi-contrast X-ray phase system based on edge illumination is investigated. It has been designed for small animal imaging and with a limited footprint for ease of deployment in laboratories. METHODS: The presented edge illumination system is based on a compact microfocus tungsten X-ray source combined with a at panel detector. The source has a maximum output of 10 W when the minimum spot size of about 15 ”m is used. The system has an overall length of 70 cm. A new double sample mask design, obtained by arranging both skipped and non-skipped configurations on the same structure, provides dual resolution capability. To test the system, we carried out CT scans of a plastic phantom with different source settings using both single-image and multi-image acquisition schemes at different spatial resolutions. In addition, CT scans of an ex-vivo mouse specimen were acquired at the best identified working conditions to demonstrate the application of the presented system to small animal imaging. RESULTS: We found this system delivers good image quality, allowing for an efficient material separation and improving detail visibility in small animals thanks to the higher signal-to-noise ratio (SNR) of phase contrast with respect to conventional attenuation contrast. The system offers high versatility in terms of spatial resolution thanks to the double sample mask design integrated into a single scanner. The availability of both multi and single image acquisition schemes coupled with their dedicated retrieval algorithms, allows different working modes which can be selected based on user preference. Multi-image acquisition provides quantitative separation of the real and imaginary part of the refractive index, however it requires a long scanning time. On the other hand, the single image approach delivers the best material separation and image quality at all the investigated source settings with a shorter scanning time but at the cost of quantitativeness. Finally, we also observed that the single image approach combined with a high-power X-ray source may result in a fast acquisition protocol compatible with in-vivo imaging
Three dimensional numerical relativity: the evolution of black holes
We report on a new 3D numerical code designed to solve the Einstein equations
for general vacuum spacetimes. This code is based on the standard 3+1 approach
using cartesian coordinates. We discuss the numerical techniques used in
developing this code, and its performance on massively parallel and vector
supercomputers. As a test case, we present evolutions for the first 3D black
hole spacetimes. We identify a number of difficulties in evolving 3D black
holes and suggest approaches to overcome them. We show how special treatment of
the conformal factor can lead to more accurate evolution, and discuss
techniques we developed to handle black hole spacetimes in the absence of
symmetries. Many different slicing conditions are tested, including geodesic,
maximal, and various algebraic conditions on the lapse. With current
resolutions, limited by computer memory sizes, we show that with certain lapse
conditions we can evolve the black hole to about , where is the
black hole mass. Comparisons are made with results obtained by evolving
spherical initial black hole data sets with a 1D spherically symmetric code. We
also demonstrate that an ``apparent horizon locking shift'' can be used to
prevent the development of large gradients in the metric functions that result
from singularity avoiding time slicings. We compute the mass of the apparent
horizon in these spacetimes, and find that in many cases it can be conserved to
within about 5\% throughout the evolution with our techniques and current
resolution.Comment: 35 pages, LaTeX with RevTeX 3.0 macros. 27 postscript figures taking
7 MB of space, uuencoded and gz-compressed into a 2MB uufile. Also available
at http://jean-luc.ncsa.uiuc.edu/Papers/ and mpeg simulations at
http://jean-luc.ncsa.uiuc.edu/Movies/ Submitted to Physical Review
A Preliminary Investigation into the Use of Edge Illumination X-ray Phase Contrast Micro-CT for Preclinical Imaging
Purpose: To enable a preliminary assessment of the suitability of edge illumination (EI) x-ray
phase contrast (XPC) micro x-ray computed tomography (micro-CT) to preclinical imaging.
Specifically, to understand how different acquisition schemes and their combination with
dedicated data processing affect contrast-to-noise ratio (CNR) and spatial resolution, while
providing control over scan time and radiation dose delivery.
Procedures: Deceased mice (n = 3) were scanned with an EI XPC micro-CT setup operated
under different settings, leading to scan times between 18 h and 13 min. For the shortest scan,
the entrance dose was measured with a calibrated PTW 23344 ion chamber. Different data
processing methods were applied, retrieving either separate attenuation and phase images, or
hybrid (combined attenuation and phase) images. A quantitative comparison was performed
based on CNR and spatial resolution measurements for a soft tissue interface.
Results: All phase-based images have led to a higher CNR for the considered soft tissue
interface than the attenuation image, independent of scan time. The best relative CNR (a sixfold
increase) was observed in one of the hybrid images. Spatial resolution was found to be
connected to scan time, with a resolution of approximately 20 ÎŒm and 60 ÎŒm achieved for the
longest and shortest scans, respectively. An entrance dose of approximately 300 mGy was
estimated for the scan performed within 13 min.
Conclusions: Despite their preliminary nature, our results suggest that EI XPC bears potential for
enhancing the utility of preclinical micro-CT, and, pending further research and development,
could ultimately become a valuable technique in this field
Key biocultural values to guide restoration action and planning in New Zealand
A pluralist and cross-cultural approach that accommodates differing values while encouraging the collaboration and social cohesion necessary for the complex task of ecological restoration is needed. We used qualitative and quantitative analyses to investigate value assigned to biocultural restoration of coastal forests in northern New Zealand by 26 interviewees from three groups (environmental managers, MÄori community members, and community project leaders). MÄori community members primarily emphasized the importance of Cultural Stewardship and Use in the restoration process, while placing less emphasis on Ecological Integrity. Otherwise, all participants shared common trends, culminating in three interrelated value sets: (1) Personal Engagement, (2) Connection, and (3) the generation and transfer of Knowledge & Wisdom. These values demonstrate that restoration's benefits to people and community are as significant as its reparations of ecological components. Despite differences, all stakeholders were united in a broadly common goal to restore socio-ecological systems. Their knowledge and shared passion for conservation signal enormous promise for accelerated and effective restoration of coastal forests, if it is conducted using a pluralistic approach. Because some values expressed were intangible and complex, with cross-cultural dimensions, current valuation tools used by ecological economists to guide management investment fail to adequately account for, in particular, MÄori values of ecological restoration.Peer Reviewe
Control of metallo-supramolecular assemblies via steric, hydrogen bonding and argentophilic interactions; formation of a 3-dimensional polymer of circular helicates
This work shows how multiple non-covalent interactions are employed to control metallosupramolecular architectures and we demonstrate that a ligand, which contains two bidentate domains separated by a ArOH spacer, forms a mesocate when complexed with Ag(I). However, changing this to an ArOCH2CH2Ph spacer unit results in a 1-dimensional helical polymer upon reaction with the same cation. Reaction of Ag(I) with the ArOMe derivative gives a hexanuclear circular helicate which forms inter-assembly AgâŻAg interactions resulting in a 3-dimensional honeycomb-like polymer of hexanuclear circular helicates
Effects of isopropanol on collagen fibrils in new parchment
Background: Isopropanol is widely used by conservators to relax the creases and folds of parchment artefacts. At present, little is known of the possible side effects of the chemical on parchments main structural component- collagen. This study uses X-ray Diffraction to investigate the effects of a range of isopropanol concentrations on the dimensions of the nanostructure of the collagen component of new parchment. Results: It is found in this study that the packing features of the collagen molecules within the collagen fibril are altered by exposure to isopropanol. The results suggest that this chemical treatment can induce a loss of structural water from the collagen within parchment and thus a rearrangement of intermolecular bonding. This study also finds that the effects of isopropanol treatment are permanent to parchment artefacts and cannot be reversed with rehydration using deionised water. Conclusions: This study has shown that isopropanol induces permanent changes to the packing features of collagen within parchment artefacts and has provided scientific evidence that its use to remove creases and folds on parchment artefacts will cause structural change that may contribute to long-term deterioration of parchment artefacts. This work provides valuable information that informs conservation practitioners regarding the use of isopropanol on parchment artefacts
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