Experiments on a thin layer of cohesive wet granular matter under vertical vibrations reveal kink separated domains that collide with the container at different phases. Due to the strong cohesion arising from the formation of liquid bridges between adjacent particles, the domains move collectively upon vibrations. Depending on the periodicity of this collective motion, the kink fronts may propagate, couple with each other and form rotating spiral patterns in the case of period tripling, or stay as standing wave patterns in the case of period doubling. Moreover, both patterns may coexist with granular 'gas bubbles' -phase separation into a liquidlike and a gaslike state. Stability diagrams for the instabilities measured with various granular layer mass m and container height H are presented. The onsets for both types of patterns and their dependency on m and H can be quantitatively captured with a model considering the granular layer as a single particle colliding completely inelastically with the container.

Industrial x-ray computed tomography (CT) represents an established measurement technique in the field of nondestructive testing and dimensional metrology. However, the measurement accuracy is sometimes limited by measurement artifacts that cannot be avoided using a standard circular scan trajectory. This problem can be addressed with the aid of flexible 3D trajectories, but up to date, the application of these is mainly restricted to special CT devices using robot arms. In this paper, we present results using a hexapod as an additional positioning system in a commercial industrial CT scanner. In addition to the 360∘ rotation, task-specific tilting of the part during the scan is possible in this way. We used and adapted geometry calibration procedures based on a multi-sphere reference object to enable reconstruction with high accuracy. Using a demonstrator test fixture with high absorbing elements, we show that severe metal and truncation artifacts can be avoided for a region-of-interest scan. Furthermore, cone-beam artifacts, which are inherent to circular scan trajectories, can be reduced significantly. Using measurement objects that can be measured well with a circular trajectory, we found that applying a 3D trajectory leads to dimensional measurement deviations in the same range or even lower than those of a circular trajectory. This suggests that the pose repeatability of the hexapod is sufficient to perform complex scan paths without general loss of accuracy. The obtained results could be relevant for end users of conventional CT scanners, as upgrading existing devices is in principle possible. The presented investigations form the basis for the application of trajectory optimization algorithms.

Thermosolutal and thermocapillary Marangoni convection at a liquid-gas interface in a microchannel structure of approximately 100 × 90 μm cross section creates a localized vortex that acts as a trap for micrometer and sub-micrometer sized tracer particles. Next to the vortex, depleted volumes appear that are entirely cleared of particles. This particle redistribution is caused by collisions of the tracers with the meniscus, which push the particles back onto the critical streamline with one particle radius distance to the meniscus. The streamlines between the meniscus and the critical streamline feed the depleted regions. Since the critical streamline depends on the particle radius, the effect leads to a particle fractionation according to their size. Diffusion allows only small particles to escape from the trap. Larger particles are permanently confined and their diffusion is rectified after every revolution at the meniscus, which produces a ratchet effect and increases the particle localization within the vortex.

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X-ray computed tomography (CT) enables dimensional measurements of numerous measurands with a single scan, including the measurement of inner structures. However, measurement artefacts complicate the applicability of the technology in some cases. This paper presents a methodology to assess the surface point quality of computed tomography measurements without the requirement of a CAD model. Measurement artefacts lowering the surface point quality can therefore automatically be detected. The correlation of quality values with the random measurement error is demonstrated. The presented method can in principle be used to weight single fit points to reduce the measurement uncertainty of CT measurements.