A GPU‐Adapted Structure for Unstructured Grids

A key advantage of working with structured grids (e.g., images) is the ability to directly tap into the powerful machinery of linear algebra. This is not much so for unstructured grids where intermediate bookkeeping data structures stand in the way. On modern high performance computing hardware, the conventional wisdom behind these intermediate structures is further challenged by costly memory access, and more importantly by prohibitive memory resources on environments such as graphics hardware. In this paper, we bypass this problem by introducing a sparse matrix representation for unstructured grids which not only reduces the memory storage requirements but also cuts down on the bulk of data movement from global storage to the compute units. In order to take full advantage of the proposed representation, we augment ordinary matrix multiplication by means of action maps, local maps which encode the desired interaction between grid vertices. In this way, geometric computations and topological modifications translate into concise linear algebra operations. In our algorithmic formulation, we capitalize on the nature of sparse matrix‐vector multiplication which allows avoiding explicit transpose computation and storage. Furthermore, we develop an efficient vectorization to the demanding assembly process of standard graph and finite element matrices.     

Ex-situ spectroscopic ellipsometry studies of micron thick CVD diamond films

Micron thick diamond films have been studied by spectroscopic ellipsometry (SE). The films were grown, on previously prepared Si(100) substrates, by the plasma enhanced chemical vapor deposition (PECVD) technique. Ex situ SE measurements were carried out on samples grown under different conditions, such as substrate temperature and methane fraction in the gas mixture. An optical model consisting of five layers was constructed in order to explain the SE spectra and to provide the optical and structural parameters of the films. This model was deduced from results of various measurements performed by other characterization techniques (Raman spectroscopy, scanning electron microscopy, atomic force microscopy and positron annihilation spectroscopy) which have revealed the optical and structural parameters of the samples. Its sensitivity to the surface and interface roughness as well as to the absorption of the nondiamond phase of the film is demonstrated. Several values of the percentage of the nondiamond phase can be obtained, with the same fit quality, however, depending on the amorphous carbon reference used in the model. These references were obtained by performing SE measurements on various amorphous carbon films. Finally, our SE analysis has allowed us to monitor the lateral homogeneity of the thickness, surface and interface roughness and nondiamond phase concentration over the diamond film.     

Protective behavior of alumina scales in sulfidizing atmospheres

Fe-17Cr steel was aluminized (three different pack-cementation treatments were used) and then oxidized before exposure to a sulfidizing (H ₂/10%H₂S) atmosphere. When the oxidation time is sufficiently high (30 min), the corrosion remains nil for a period termed the immunity time. The corrosion initiates by sulfur diffusion through the alumina scale, which had been formed previously. A diffusion model was established: the sulfur diffusion coefficient in the oxide depends on the oxidation duration and on the aliminizing treatment. Its activation energy was calculated to be 353 kJ and was constant regardless of the prior cementation treatment.     

Subdivision-Specialized Linear Algebra Kernels for Static and Dynamic Mesh Connectivity on the GPU

Subdivision surfaces have become an invaluable asset in production environments. While progress over the last years has allowed the use of graphics hardware to meet performance demands during animation and rendering, high-performance is limited to immutable mesh connectivity scenarios. Motivated by recent progress in mesh data structures, we show how the complete Catmull-Clark subdivision scheme can be abstracted in the language of linear algebra. While this high-level formulation allows for a fully parallel implementation with significant performance gains, the underlying algebraic operations require further specialization for modern parallel hardware. Integrating domain knowledge about the mesh matrix data structure, we replace costly general linear algebra operations like matrix-matrix multiplication by specialized kernels. By further considering innate properties of Catmull-Clark subdivision, like the quad-only structure after refinement, we achieve an additional order of magnitude in performance and significantly reduce memory footprints. Our approach can be adapted seamlessly for different use cases, such as regular subdivision of dynamic meshes, fast evaluation for immutable topology and feature-adaptive subdivision for efficient rendering of animated models. In this way, patchwork solutions are avoided in favor of a streamlined solution with consistent performance gains throughout the production pipeline. The versatility of the sparse matrix linear algebra abstraction underlying our work is further demonstrated by extension to other schemes such as and Loop subdivision.     

Impact evaluation of the voluntary early retirement policy on research and technology outputs of the faculties of science in Morocco

Scientometric indicators or science metrics, conventional and derived ones, are used in ex-post evaluating of a government policy with impact on research system. Publications, citations, h-index, Glänzel model, and patents are applied in both micro and meso levels. This provides useful insight into the impact of the voluntary early retirement policy on research and technological outputs of the faculties of science in Morocco and consequently on the overall Morocco??s research system. The use of these metrics showed that the effect of the initiative was quite limited by affecting an average of 8% of the professor staffs of these institutions. Furthermore, each professor benefiting from this initiative had produced an average of 3.7 publications indexed in SCI in all his (her) career. The few number of the publications attributed to these professors had been gradually decreasing even 6 years before the initiative. No specific scientific field had intensively been struck. The findings also support that these professors were in general more ??author?? than ??inventor??. Inventor-professor institutions were likely more affected by the initiative. By means of these metrics, even if the initiative had not contributed to rejuvenate the professor-staffs of the faculties of science in Morocco, would nevertheless be a stimulus of their research system with respect to their scientometric indicators.     

Interactive Modeling of Cellular Structures on Surfaces with Application to Additive Manufacturing

The rich and evocative patterns of natural tessellations endow them with an unmistakable artistic appeal and structural properties which are echoed across design, production, and manufacturing. Unfortunately, interactive control of such patterns-as modeled by Voronoi diagrams, is limited to the simple two dimensional case and does not extend well tofreeform surfaces. We present an approach for direct modeling and editing of such cellular structures on surface meshes. The overall modeling experience is driven by a set of editing primitives which are efficiently implemented on graphics hardware. We feature a novel application for 3D printing on modern support-free additive manufacturing platforms. Our method decomposes the input surface into a cellular skeletal structure which hosts a set of overlay shells. In this way, material saving can be channeled to the shells while structural stability is channeled to the skeleton. To accommodate the available printer build volume, the cellular structure can be further split into moderately sized parts. Together with shells, they can be conveniently packed to save on production time. The assembly of the printed parts is streamlined by a part numbering scheme which respects the geometric layout of the input model.     

Mesh segmentation driven by Gaussian curvature

Mesh parameterization is a fundamental problem in computer graphics as it allows for texture mapping and facilitates many mesh processing tasks. Although there exists a variety of good parameterization methods for meshes that are topologically equivalent to a disk, the segmentation into nicely parameterizable charts of higher genus meshes has been studied less. In this paper we propose a new segmentation method for the generation of charts that can be flattened efficiently. The integrated Gaussian curvature is used to measure the developability of a chart, and a robust and simple scheme is proposed to integrate the Gaussian curvature. The segmentation approach evenly distributes Gaussian curvature over the charts and automatically ensures a disklike topology of each chart. For numerical stability, we use an area on the Gauss map to represent Gaussian curvature. The resulting parameterization shows that charts generated in this way have less distortion compared to charts generated by other methods.     

"Crossed-field" excitation of an acoustic superlattice with matched boundaries: theory and experiment

Electrical characteristics of a new type of acoustic transducer have been investigated theoretically and experimentally. The agreement between calculated and measured results is excellent. The transducer consists of an acoustic superlattice, made of periodically poled LiNbO/sub 3/ (PPLN), with acoustically matched boundaries, facilitating the construction of acousto-optic (AO) devices through monolithic integration.