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31.
Teaching meshes, subdivision and multiresolution techniques   总被引:2,自引:0,他引:2  
In recent years, geometry processing algorithms that directly operate on polygonal meshes have become an indispensable tool in computer graphics, CAD/CAM applications, numerical simulations, and medical imaging. Because the demand for people that are specialized in these techniques increases steadily the topic is finding its way into the standard curricula of related lectures on computer graphics and geometric modeling and is often the subject of seminars and presentations. In this article we suggest a toolbox to educators who are planning to set up a lecture or talk about geometry processing for a specific audience. For this we propose a set of teaching blocks, each of which covers a specific subtopic. These teaching blocks can be assembled so as to fit different occasions like lectures, courses, seminars and talks and different audiences like students and industrial practitioners. We also provide examples that can be used to deepen the subject matter and give references to the most relevant work.  相似文献   
32.
Inplane tensile fracture of unnotched and notched thermoset graphite-epoxy and thermoplastic graphite-PEEK composite laminates is examined. Both fibre-dominated quasi-isotropic and matrix dominated ±45 angle-ply layups were investigated.Classical lamination theory predictions of elastic and strength properties of unnotched specimens are compared with experiments. Several notched geometries, i.e. centre-notched, double-edge notched and open-hole specimens subjected to tensile loading to fracture were examined. The notched strength of the quasi-isotropic laminates was analysed by a damage zone model, where damage around the notch is represented by an equivalent crack with cohesive force acting between the crack surfaces.Good agreement between experimental and calculated strength was observed for the graphite-epoxy laminates which failed in a collinear manner. For the graphite-PEEK laminates discrepancies between predicted and experimental strength are related to observed deviations from collinear crack growth. The angle-ply graphite-PEEK laminates showed larger notch sensitivity than the corresponding graphite-epoxy, probably due to less degree of stress relieving damage formation around the notch.  相似文献   
33.
Principal components analysis (PCA) is useful for reproducing the total variation among hundreds or thousands of continuously-scaled variables with a much smaller number of unobservable variables called 'latent factors'. The CLUSFAVOR computer program was used to implement PCA for identifying groups of genes with similar expression profiles from a large number of genes used on DNA microarrays. This paper describes the principal components solution to the factor model of the correlation matrix R, calculation of eigenvalues and eigenvectors of R, extraction of factors, and calculation of factor loadings and identification of genes with similar loading patterns to construct groups of genes with similar expression profiles. With regard to extraction of factors, it was found that more than 90% of the total variance in input data could be accounted for by extracting factors whose eigenvalues exceed unity. Bipolar factors containing strong positive and negative loadings can also be used for identifying two unique groups of genes, since expression profiles of genes that load positive are unlike expression profiles of genes that load negative on the same factor. While PCA does not provide the absolute answer to a multidimensional problem, it nevertheless can provide a heuristic with which natural groupings of genes with similar expression profiles can be assembled. While cluster analysis essentially generates a single dendogram (tree branch) containing every gene in the input data, PCA can be used to assemble gene expression profiles that strongly correlate with the latent factors accounting for a majority of total variance. Example results for CLUSFAVOR computer program runs are provided.  相似文献   
34.
Nuclear fusion D+D processes are studied by nanosecond pulsed laser interaction with ultra-dense deuterium. This material has a density of 1029 cm?3 as shown in several previous publications. Laser power is <2 W (0.2 J pulses) and laser intensity is <1014 W cm?2 in the 5–10 μm wide beam waist. Particle detection by time-of-flight energy analysis with plastic scintillators is used. Metal foils in the particle flux to the detector remove slow ions, and make it possible to convert and count particles with energy well above 1 MeV. The variation of the signal of MeV particles from D+D fusion is measured as a function of laser power. At relatively weak laser-emitter interaction, the particle signal from the laser focus varies as the square of the laser power. This indicates collisions in the ultra-dense deuterium of two fast deuterons released by Coulomb explosions. During experiments with stronger laser-emitter interaction, the signal varies approximately as the sixth power of the laser power, indicating a plasma process. At least 2 × 106 particles are created by each laser pulse at the maximum intensity used. Our results indicate break-even in fusion at a laser pulse energy of 1 J with the same focusing, in approximate agreement with theoretical results for ignition conditions in ultra-dense deuterium. Radiation loss at high temperature will however require higher laser energy at break-even.  相似文献   
35.
Efficient surface reconstruction and reverse engineering techniques are usually based on a polygonal mesh representation of the geometry: the resulting models emerge from piecewise linear interpolation of a set of sample points. The quality of the reconstruction not only depends on the number and density of the sample points but also on their alignment to sharp and rounded features of the original geometry. Bad alignment can lead to severe alias artifacts. In this paper we present a sampling pattern for feature and blend regions which minimizes these alias errors. We show how to improve the quality of a given polygonal mesh model by resampling its feature and blend regions within an interactive framework. We further demonstrate sophisticated modeling operations that can be implemented based on this resampling technique.  相似文献   
36.
The behaviour of paperboard beams subjected to pure bending is analysed and related to tensile and compression stress-strain behaviour. Since the compression strength is lower than the tensile strength, beam failure occurs in compression. However, beam failure does not occur when the ultimate strain in pure compression is reached in the surface fibres. A plastic yielding in compression, which gives good agreement between experimentally-determined and theoretically-calculated bending moments up to failure is therefore suggested. At failure, the elastic energy stored in the sample causes propagation of an interlaminar crack at the compression side, which is observed in scanning electron micrographs.  相似文献   
37.
This paper reports practical experience in implementing Alice, an extension of Standard ML, on top of an existing implementation of Oz. This approach yields a high-quality implementation with little effort. The combination is an advanced programming system for both Oz and Alice, which offers more than either language on its own.Many thanks go to Ulrike Becker-Kornstaedt, Thorsten Brunklaus, Tobias Müller, and Christian Schulte for their comments on a previous version of this paper. For the numerous discussions regarding the details of the translation scheme, thanks go to Andreas Rossberg, implementor of the Alice compiler frontend. Finally, I'd like to thank the anonymous referees for their commments.  相似文献   
38.
Adaptive QRS Detection: A Study of Performance   总被引:2,自引:0,他引:2  
QRS detectors are often evaluated in terms of statistical measures, e.g., rate of false and true detections. These measures are usually calculated for a detector with fixed parameter values. In this paper, detector properties are studied by varying those parameters which seem to have the most profound effect on performance. By applying techniques known from optimal estimation to a stochastic model for the ECG, two different detectors have been derived. The detector structures are described in detail. In order to study and compare the performance of the two detectors, a database of "difficult" ECG's has been collected, containing various "artifacts" of physiological and electrical/mechanical origin. The performance of this database is presented in terms of receiver-operating characteristics (ROC's), and several examples are discussed.  相似文献   
39.
Heat flux differential scanning calorimetry (DSC) and electron spin resonance spectroscopy (ESR) were used to assess the activity and the thermal stability of antioxidants in four vegetable oils. Sunflower oil (SO) and high oleic sunflower oil (HOSO), both rich in diunsaturated fatty acids (FA), low trans oil (LT) and partially hydrogenated palm oil (PHPO), both containing monounsaturated FA, were analyzed by isothermal heat flux DSC, with or without 300 mg/kg of antioxidant: ascorbyl palmitate (AP), α-tocopherol (αT), δ-tocopherol (δT) and propyl gallate (PG). DSC experiments showed that δT is the most effective antioxidant for SO and PG for the less unsaturated oils. SO and PHPO were also analyzed by ESR at 120 and 145 °C, respectively. ESR results confirm the strongest antioxidant activity of δT and PG for SO and PHPO, respectively. Therefore, the present study demonstrates that DSC and ESR are valuable technologies to study activity and stability of antioxidants at high temperature. Moreover, experiments performed in the presence of the spin-trap N-tert-butyl-α-phenylnitrone (PBN), suggest that δT delay lipid oxidation through a different reaction mechanism when compared to αT. A different mechanism between tocopherols isomers in delaying lipid oxidation has been hypotized.  相似文献   
40.
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