A Shift Selection Strategy for Parallel Shift-invert Spectrum Slicing in Symmetric Self-consistent Eigenvalue Computation

© 2020 ACM. The central importance of large-scale eigenvalue problems in scientific computation necessitates the development of massively parallel algorithms for their solution. Recent advances in dense numerical linear algebra have enabled the routine treatment of eigenvalue problems with dimensions on the order of hundreds of thousands on the world's largest supercomputers. In cases where dense treatments are not feasible, Krylov subspace methods offer an attractive alternative due to the fact that they do not require storage of the problem matrices. However, demonstration of scalability of either of these classes of eigenvalue algorithms on computing architectures capable of expressing massive parallelism is non-trivial due to communication requirements and serial bottlenecks, respectively. In this work, we introduce the SISLICE method: a parallel shift-invert algorithm for the solution of the symmetric self-consistent field (SCF) eigenvalue problem. The SISLICE method drastically reduces the communication requirement of current parallel shift-invert eigenvalue algorithms through various shift selection and migration techniques based on density of states estimation and k-means clustering, respectively. This work demonstrates the robustness and parallel performance of the SISLICE method on a representative set of SCF eigenvalue problems and outlines research directions that will be explored in future work

Imaging slow failure in triaxially deformed Etna basalt using 3D acoustic-emission location and X-ray computed tomography

We have deformed basalt from Mount Etna (Italy) in triaxial compression tests under an effective confining pressure representative of conditions under a volcanic edifice (40 MPa), and at a constant strain rate of 5 similar to 10(-6) s(-1). Despite containing a high level of pre-existing microcrack damage, Etna basalt retains a high strength of 475 MPa. We have monitored the complete deformation cycle through contemporaneous measurements of axial strain, pore volume change, compressional wave velocity change and acoustic emission (AE) output. We have been able to follow the complete evolution of the throughgoing shear fault without recourse to any artificial means of slowing the deformation. Locations of AE events over time yields an estimate of the fault propagation velocity of between 2 and 4 mm. s(-1). We also find excellent agreement between AE locations and post-test images from X-ray microtomography scanning that delineates deformation zone architecture

Imaging compaction band propagation in Diemelstadt sandstone using acoustic emission locations

We report results from a conventional triaxial test performed on a specimen of Diemelstadt sandstone under an effective confining pressure of 110 MPa; a value sufficient to induce compaction bands. The maximum principal stress was applied normal to the visible bedding so that compaction bands propagated parallel to bedding. The spatio-temporal distribution of acoustic emission events greater than 40 dB in amplitude, and associated with the propagation of the first compaction band, were located in 3D, to within +/- 2 mm, using a Hyperion Giga-RAM recorder. Event magnitudes were used to calculate the seismic b- value at intervals during band growth. Results show that compaction bands nucleate at the specimen edge and propagate across the sample at approximately 0.08 mm s(-1). The seismic b-value does not vary significantly during deformation, suggesting that compaction band growth is characterized by small scale cracking that does not change significantly in scale

The distribution of the dwarf succulent genus Conophytum N.E.Br. (Aizoaceae) in southern Africa.

Background: The dwarf succulent genus Conophytum N.E.Br. is one of the most speciose in the Aizoceae. The genus is most closely associated with a region of high floral endemism and biodiversity, namely the Succulent Karoo biome in Southwestern Africa. Objectives: To examine the distribution of Conophytum in Southwestern Namibia and in the Northern and Western Capes of South Africa. Method: A database consisting of 2,798 locality records representing all known species and subspecies of the genus Conophytum has been constructed. Results: The genus is primarily restricted to the arid winter rainfall region of the Northern and Western Cape of South Africa and southwestern Namibia within the Greater Cape Floristic Region. Whilst taxa are found across all the main biomes in the region (the Succulent Karoo, Nama Karoo, Desert and Fynbos biomes), 94% of Conophytum taxa are found only in the Succulent Karoo biome, and predominantly (88% of taxa) within South Africa. Endemism within specific bioregions is a feature of the genus and ~60% of taxa are endemic to the Succulent Karoo alone. Approximately 28% of all taxa could be considered point endemics. Whilst the genus has a relatively wide geographical range a pronounced centre for endemism has been identified in the southern Richtersveld. Conclusion: That the genus Conophytum can be used as a good floral model for studying patterns of diversity and speciation in the Succulent Karoo biome; the effects of climate change on dwarf succulents; as well as informing conservation planning efforts

Analysis of the functional morphology of mouthparts of the beetle Priacma serrata, and a discussion of possible food sources.

PublishedJournal ArticleWith the help of scanning electron microscopy, high resolution X-ray tomography (µCT), and finite element analysis, the mechanical and functional properties of the mandibles and associated muscles of the beetle Priacma serrata (LeConte) (Coleoptera: Archostemata) were studied. The combination of these techniques allowed for studying mechanical properties of the headmandible- system without using living animals. The µCT analysis delivered precise volumetric data of the geometry of the system to be studied. Dimensions of the cuticle of the parts involved could be readily deduced from the µCT-data. Thus, an exact representation of the specimen without significant artifacts like deformations and misalignments, usually resulting from histological sectioning, could be reconstructed. A virtual 3D model built from these data allowed for investigating different stress scenarios with finite element analysis. Combining these methods showed that P. serrata most likely uses its robustly-built mandibles for cutting hard material. In combination with available information on its habitat, possible food sources are discussed.The authors are grateful for the help provided by Freek Pasop of SkyScan in preparing the µCT data of Priacma serrata and for the very helpful comments on the manuscript by Benjamin Wipfler and an anonymous reviewer. A collecting trip of T. Hörnschemeyer to Montana, USA, was financially supported by the DAAD (D/96/05967). T. Hörnschemeyer was supported by a DFG Heisenberg grant HO 2306/6-1,2. T. Hörnschemeyer wishes to thank Mike Ivy, Montana State University, Bozeman, Montana, USA, for his generous general support

Children in Brunei Darussalam: their educational, legal and social protections

The past two decades of academic work, have cemented the idea that childhood is a social construction. As such, how children are conceptualized, educated, protected and interacted with differs from society to society, given the values inherent in each social construction. Culture, history and geography all influence the daily lives of children, and the inherent protections that children are offered in each society. This paper examines child protection provisions embedded in Brunei Darussalam by critically reviewing the sparse literature available. While much academic work has been done on Brunei Darussalam’s political system and unique ideology, little has been written on the children of Brunei. Specifically, the focus taken is on the protections offered by the Bruneian legal and education systems, family and cultural institutions, and on Brunei’s international commitments to ensuring child wellbeing

Laboratory Simulation of Volcano Seismicity

The physical processes generating seismicity within volcanic edifices are highly complex and not fully understood. We report results from a laboratory experiment in which basalt from Mount Etna volcano (Italy) was deformed and fractured. The experiment was monitored with an array of transducers around the sample to permit full-waveform capture, location, and analysis of microseismic events. Rapid post-failure decompression of the water-filled pore volume and damage zone triggered many low-frequency events, analogous to volcanic long-period seismicity. The low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample; these events exhibited a weak component of shear (double-couple) slip, consistent with fluid-driven events occurring beneath active volcanoes

Biodiversity and climate change: Risks to dwarf succulents in Southern Africa.

The aim of this study was to explore the effects of anthropogenic climate change on the dwarf succulent genus Conophytum (Aizoaceae) within areas recognised for their floral biodiversity, namely the Succulent Karoo, Fynbos, Desert and Nama Karoo biomes of South Africa and Namibia. Niche-based modelling was used to identify the key climatic and geological variables influencing the distribution of members of the genus Conophytum. The distribution of the genus is primarily controlled by a small number of environmental variables, notably winter and summer rainfall levels, together with geology. Assuming a zero-dispersal model, the predicted effect of both the A1B and A2 climatic emission scenarios was a severe contraction in the area satisfying the bioclimatic envelope for the genus coupled with significant range dislocation. Reductions of >90% in suitable habitat for 10 of the 16 taxonomic Sections that comprise the genus and represent >80% of taxa under the A2 scenario are predicted. Under A1B the projected effects are ameliorated, but reductions of >50% of habitat can be seen in a majority of Sections. Significant projected reductions in the habitable bioclimatic envelope are very likely to increase risk of extinction of ~80% of taxa even under a partly mitigated emissions scenario

Image-based software solutions for advanced materials processing and characterization

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordNew image-based solutions are being developed for advanced materials processing and characterization, which involve working with and creating high-quality models from scan data (such as MRI, CT, micro-CT…). Techniques involving the reconstruction and analysis of 3D materials data can accurately reconstruct internal structures, even to the nano level, and generate high-quality meshes suitable for design and simulation applications. By looking at key techniques and their applications, it is possible to better understand the wider impact and benefits of image-based modelling for industry when working with advanced materials

The mechanics of decompressive craniectomy: Personalized simulations

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordDecompressive craniectomy is a traditional but controversial surgical procedure that removes part of the skull to allow an injured and swollen brain to expand outward. Recent studies suggest that mechanical strain is associated with its undesired, high failure rates. However, the precise strain fields induced by the craniectomy are unknown. Here we create a personalized craniectomy model from magnetic resonance images to quantify the strains during a decompressive craniectomy using finite element analysis. We swell selected regions of the brain and remove part of the skull to allow the brain to bulge outward and release the intracranical swelling pressure. Our simulations reveal three potential failure mechanisms associated with the procedure: axonal stretch in the center of the bulge, axonal compression at the edge of the craniectomy, and axonal shear around the opening. Strikingly, for a swelling of only 10%, axonal strain, compression, and shear reach local maxima of up to 30%, and exceed the reported functional and morphological damage thresholds of 18% and 21%. Our simulations suggest that a collateral craniectomy with the skull opening at the side of swelling is less invasive than a contralateral craniectomy with the skull opening at the opposite side: It induces less deformation, less rotation, smaller strains, and a markedly smaller midline shift. Our computational craniectomy model can help quantify brain deformation, tissue strain, axonal stretch, and shear with the goal to identify high-risk regions for brain damage on a personalized basis. While computational modeling is beyond clinical practice in neurosurgery today, simulations of neurosurgical procedures have the potential to rationalize surgical process parameters including timing, location, and size, and provide standardized guidelines for clinical decision making and neurosurgical planning.This work was supported by the Wolfson/Royal Society Merit Award to Alain Goriely and by the National Institutes of Health grant U01 HL119578 to Ellen Kuhl