Giant bubble pinch-off

Self-similarity has been the paradigmatic picture for the pinch-off of a drop. Here we will show through high-speed imaging and boundary integral simulations that the inverse problem, the pinch-off of an air bubble in water, is not self-similar in a strict sense: A disk is quickly pulled through a water surface, leading to a giant, cylindrical void which after collapse creates an upward and a downward jet. Only in the limiting case of large Froude number the neck radius $h$ scales as $h(-\log h)^{1/4} \propto \tau^{1/2}$, the purely inertial scaling. For any finite Froude number the collapse is slower, and a second length-scale, the curvature of the void, comes into play. Both length-scales are found to exhibit power-law scaling in time, but with different exponents depending on the Froude number, signaling the non-universality of the bubble pinch-off.Comment: 5 pages, 2 figures. Figure quality was reduced considerably and converted to greyscale to decrease file siz

Toward a Theology of Christian Worship and the Improvement of Worship Participation in Seventh-day Adventist Churches in Africa

In the typical mission station in West Africa in the nineteenth and even in the early twentieth century, life was routinely patterned after the Western mode, hardly reflecting at all the life and routine of the surrounding villages. This was particularly true of their worship. It is the thesis of this doctoral project that an effective approach to promoting and advancing African Christianity is to proclaim the basic principles of Christian worship and faith in such a way that these principles can be understood and lived in any society or culture. Christian worship must be seen as transcending ethnic and cultural barriers. It was the purpose, of this project to introduce these basic principles of worship to the student body and faculty of the Adventist Seminary of West Africa. This school was viewed as having the potential to play a key role through its graduates in influencing the worship patterns of the church in Africa. An extensive statement of a theological nature was prepared as a position paper on worship and constitutes the first part of this report. The practical application of the implications stemming from this statement is reported in the second part of this paper. Certain key concepts are extrapolated from the position paper as the basis for a program of education for worship. Recommendations for incorporating such a program at A.S.W. A. included preaching (as at a student Week of Spiritual Emphasis), the formation of a worship committee, a worship seminar/workshop, Bible-study groups, and a prayer-meeting study series. The first; steps in the implementation of such a program were taken in a Week of Spiritual Emphasis during which twelve sermons on the subject were presented. The activities of this special week are reported, evaluated, and analyzed in this report

Partitioning 3D space for parallel many-particle stimulations

In a common approach for parallel processing applied to simulations of manyparticle systems with short-ranged interactions and uniform density, the simulation cell is partitioned into domains of equal shape and size, each of which is assigned to one processor. We compare the commonly used simple-cubic (SC) domain shape to domain shapes chosen as the Voronoi cells of BCC and FCC lattices. The latter two are found to result in superior partitionings with respect to communication overhead. Other domain shapes, relevant for a small number of processors, are also discussed. The higher eciency with BCC and FCC partitionings is demonstrated in simulations of the sillium model for amorphous silicon

Automated dose evaluation on daily cone-beam computed tomography for breast cancer patients

Background and purpose: Our goal was to develop a workflow to automatically evaluate delivered dose on daily cone beam computed tomography (CBCT) in all breast cancer patients to assess dosimetric impact of anatomical changes and guide decision-making for offline plan adaptation. Materials and methods: The workflow automatically processes the daily CBCTs of all breast cancer patients receiving local and locoregional radiotherapy. The planning-CT is registered to the CBCT to create a synthetic CT and propagate contours. A forward dose calculation is performed, and DVH parameters are extracted and printed in a report. We evaluated the workflow on a group level and in a subset of 30 patients on a patient-specific level, including comparison to clinical evaluation on additional planning-CT in 10 patients. Results: 7454 fractions in 647 patients were analyzed over a period of seven months. Median breast clinical target volume V95% was ≥ 95 % for 97 % of the patients. The workflow would have provided useful additional insights for decision-making for the requirement of plan adaptation, based on debatable disagreement with the clinical decision in half of the cases with an additional planning-CT. The workflow also identified cases with suboptimal coverage not identified in the clinical procedure. Conclusion: We developed a fully automated workflow for dose evaluation on daily CBCT for local and locoregional breast radiotherapy. We have demonstrated its potential for aiding decision-making for plan adaptation in patients with changing anatomy and its capability to highlight patients that may receive suboptimal treatment and require closer clinical evaluation of treatment quality

Towards device-size atomistic models of amorphous silicon

The atomic structure of amorphous materials is believed to be well described by the continuous random network model. We present an algorithm for the generation of large, high-quality continuous random networks. The algorithm is a variation of the "sillium" approach introduced by Wooten, Winer, and Weaire. By employing local relaxation techniques, local atomic rearrangements can be tried that scale almost independently of system size. This scaling property of the algorithm paves the way for the generation of realistic device-size atomic networks.Comment: 7 pages, 3 figure