Dynamic micro-CT analysis of fracture formation in rock specimens subjected to multi-phase fluid flow

In this study, fracture formation in rocks is being studied at the pore-scale through the combination of high-resolution X-ray CT scanning with custom-made add-on modules. The Deben CT5000 system, an in-situ load cell, was used at the scanners at the Centre for X-ray Tomography at Ghent University (UGCT), providing information on mechanical properties of the tested rocks. Micro-CT scans made at the High Energy CT system Optimised for Research (HECTOR) allowed the visualisation of the fracturesk and their formation as well as the analysis of porosity changes in the material, related to the changes in stress

Financial Operational Losses in Space Launch

The high cost of access to space has been a problem since the beginning of the space age. Most attempts to reduce this cost are centered on improvements to launch vehicle design. While this approach has been fruitful, less attention has been paid to other causes of high cost. Two of these are wastage of launch vehicle payload capacity and use of cost-ineffective launch vehicles. Both of these are associated with the way the launch vehicles are operated, and so are operational losses. This work examines the extent of operational losses in space launch over the period January 1, 2000, to September 29, 2013, and considers strategies for reducing these losses. The cumulative worldwide wastage for this period was 654 tons, which is 20.4% of total payload capacity, and represents a financial loss of no less than $8.72 billion (2014$). The cumulative loss due to cost-ineffective launch vehicle selection is less certain, but is no greater than 43.8% of total launch cost, or $19.3 billion. Two possible strategies may combat operational losses: changing launch vehicle selection or rearranging payloads. Changing launch ve- hicle selection can in principle eliminate cost-ineffective launch vehicle use, but is prevented in some measure by non-economic considerations. Rearrangement of payloads cannot eliminate wastage, but can reduce it considerably, to as little as 2% in some cases. Combining these two strategies by applying a bin-packing algorithm to the set of launch vehicles and payloads can yield a considerable cost savings, reducing total launch costs to geosynchronous orbit by as much as 53% if both launch vehicle selection and payload arrangement are unrestricted. Even in the most restrictive scenario where payloads must be launched in the same calendar year they actually were and launch vehicle choice is restricted to the launch vehicles actually used during that year, cost savings of 19.1% over the actual launches are possible

Investigating the influence of dynamic effects on two-phase flow at the pore scale with fast laboratory-based X-ray micro-CT

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Use of freeze-cracking in ontogenetic research in Macrostomum lignano (Macrostomida, Rhabditophora)

A method for studying whole mount flatworm embryos based on freeze-cracking of the eggs is described. This method allows successful immunohistological and immunocytological studies of whole mount embryos. It does not require the use of sharpened needles or a microinjection system to puncture the eggshell. Moreover, this method is more practical and less time-consuming than classical puncturing and much cheaper than the use of a microinjection system. The advantages of this method are illustrated by results of several immunolocalisation experiments in the macrostomid flatworm Macrostomum lignano. The optimal procedure and crucial steps for this method are discussed

Effect of an initial solution in iterative reconstruction of dynamically changing objects

Visualizing and analyzing dynamic processes in 3D is an emerging topic, e.g. in geosciences (Berg et al., 2009; Cnudde and Boone, 2013; Bultreys et al., accepted), which has only recently become possible due to fast, high-resolution CT scanning. However; dynamically changing objects pose a challenge in CT-imaging because the existing reconstruction algorithms, which reconstruct the sample volume from a number of scan images, presume an unchanging sample during the acquisition of the projection images. Movements or changes during the scan cause artefacts in the resulting volume. Furthermore, when fast processes are visualized, the acquisition time needs to be reduced, thus drastically decreasing the signal-to-noise ratio (SNR). To address these issues, an iterative reconstruction technique is applied, where an initial solution is provided to the algorithm. In this work, we present an evaluation of this method based on both simulations and real experimental data

Improving the reconstruction of dynamic processes by including prior knowledge

Visualizing and analyzing dynamic processes in 3 dimensions is an increasingly important topic. High-resolution CT-scanning is a suitable technique for this, as it is non-destructive and therefore does not hinder the dynamic process while it is advancing. However, CT reconstruction algorithms, which reconstruct a 3D volume from a series of projection images, assume a static sample. Motion artefacts are introduced when this assumption is invalid. This is usually solved by dividing the set of projection images in smaller subsets, each representing a time frame in which the change to the sample is assumed to be sufficiently small. Each subset can be reconstructed separately. However, due to the small size of the subsets and/or the high speed (and therefore lower statistics and higher noise) at which is scanned, the reconstruction quality is reduced. One method to improve reconstruction quality is using a priori knowledge. Of the two most used reconstruction algorithms, the iterative reconstruction scheme is best suited for this. The simultaneous algebraic reconstruction technique or SART starts from a (typically empty) volume and improves this gradually by back projecting the difference between a simulated projection from this volume and the measured projection. The resulting volume is used for the next iteration step. After a number of iterations, the solution converges to the final volume which represents the sample. In this research, this algorithm is used and adapted to take prior knowledge into account. Prior knowledge can take various forms. Using an initial volume (to start the reconstruction algorithm with) that resembles the sample is the most well-known and already presents a great improvement. This can be a volume that is reconstructed from a previous scan of the same sample, before the dynamic process is initiated, or one from after the process has finished. It is also possible to incorporate information in the algorithm about the regions in the volume where the changes are most likely to occur. The voxels in these regions are assigned a higher contribution from the back projection in comparison with their 'static' neighboring voxels which are assumed to be valid in the initial volume. This reduces the number of projections needed significantly. These forms of prior knowledge already pose a great improvement to the reconstruction quality, as is shown by the preliminary results. There are however numerous other possibilities to improve the reconstruction of dynamic processes. Other forms of prior knowledge, e.g. the continuity of changes or external measurements, can be included. Spatio-temporal correlations present another way to improve 4D-reconstruction. The projections will no longer be divided into completely separate subsets. Instead, the correlations between different projections will be used. This means that projections 'far' away from the time point that is being reconstructed will also (partially) be included. In this way the limitation of a small subset is (partially) removed, since much larger sets of projections are considered. The reconstructions that lie some time away from the reconstruction point cannot be straightforwardly included, since this would include exactly the artefacts that made the scanning of dynamic processes hard in the first place. This is a subject of further and current research. REFERENCES [1] M. Beister, D. Kolditz, W. A. Kalender, “Iterative reconstruction methods in X-ray CT,” Physica Medica, vol. 28, no. 2, pp. 94-108, Apr. 2012. [2] S. Berg, H. Ott, S. A. Klapp, A. Schwing, R. Neiteler, N. Brussee, A. Makurat, L. Leu, F. Enzmann, J.-O. Schwarz, “Real-time 3D imaging of Haines jumps in porous media flow,” Proc Natl Acad Sci U S A, vol. 110(10), pp. 3755–3759, Mar. 2013. [3] T. Bultreys, M. A. Boone, M. N. Boone, T. De Schryver, B. Masschaele, L. Van Hoorebeke, V. Cnudde, “Fast laboratory-based micro-computed tomography for pore-scale research: illustrative experiments and perspectives on the future,” Adv. Wat. Res., In Press. Available online May 2015. [4] V. Cnudde, M. N. Boone, “High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications,” Earth-Science Reviews, vol. 123, pp. 1-17, Aug. 2013. [5] G. Van Eyndhoven, K. J. Batenburg, J. Sijbers, “Region-based iterative reconstruction of structurally changing objects in CT”, IEEE Trans. Image Processing, vol. 23, no. 2, pp. 909-919, Feb. 2014. [6] L. Brabant, “Latest developments in the improvement and quantification of high resolution X-ray tomography data,” Ph.D. dissertation, Dep. Phys. and Astr., Fac. Sciences, Ghent Univ., Ghent, Belgium, 2013

Pore-scale wettability characterization in mixed-wetsandstones using dynamic laboratory micro X-raytomography

Multiphase flow is strongly influenced by the wettability of the porous medium. Conventionally, wettability is quantified by the contact angle between the fluid-fluid interface and the solid surface. Recent attempts to measure contact angles directly (AlRatrout et al., 2017; Scanziani et al., 2017) and indirectly (Blunt et al., 2019) from micro X-ray tomographic images have proven to be challenging due to the scale-dependent and hysteretic nature of contact angles. In principle, the contact angle that controls the invasion process has to be measured at (or at least near) the moment the fluid interface moves into a neighboring pore. Laboratory based dynamic micro X-ray tomography (Bultreys et al., 2016) offers the possibility to perform challenging experiments in a controlled laboratory environment, with acquisition times and image quality close to those achieved at synchrotron facilities. For this study, n-decane-brine drainage and imbibition experiments were performed on two medium-grained calcareous sandstone samples from the Luxembourg Sandstone Formation (lower Jurassic). One of these samples was treated using octadecyltrichlorosilane (OTS) to induce an intermediate to mixed wettability distribution. The experiments were imaged continuously using a laboratory based micro X-ray tomography scanner optimized for fast image acquisition to generate a time series of micro-CT images. For each image, pore-scale properties such as fluid distributions, fluid-fluid interfacial curvatures and contact angles were calculated. Using a clustering algorithm, neighboring pores that change fluid occupancy are clustered together allowing calculations of pore-scale properties on an event-by-event basis. Measurements of the pore scale properties are validated by performing high resolution region of interest scans (2um/voxel) at the end of drainage and imbibition. By combining image-based pore-scale properties with spatial connectivity information, wettability can be characterized at the pore-scale to inform numerical simulations of multiphase flow