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51.
We analyze the behavior of a dense granular aggregate made by identical, elastic spheres, uni-axially compressed at constant pressure. Our goal is to predict the evolution of the effective moduli along the loading path when small perturbations are applied to stressed states. The analytical model is based upon the average strain theory. We show that the moduli in the anisotropic state normalized with the corresponding initial isotropic value, are captured by a so crude model. Numerical simulations support this result. 相似文献
52.
Marianne Richou Marc Missirlian Nicolas Vignal Vincent Cantone Caroline Hernandez Prachai Norajitra Luigi Spatafora 《Fusion Engineering and Design》2013,88(9-10):1753-1757
Plasma facing components (PFCs) with tungsten (W) armor materials for DEMO divertor require a high heat flux removal capability (at least 10 MW/m2 in steady-state conditions). The reference divertor PFC concept is a finger with a tungsten tile as a protection and sacrificial layer brazed to a thimble made of tungsten alloy W – 1% La2O3 (WL10). Defects may be located at the W thimble to W tile interface. As the number of fingers is considerable (>250,000), it is then a major issue to develop a reliable control procedure in order to control with a non-destructive examination the fabrication processes. The feasibility for detecting defect with infrared thermography SATIR test bed is presented. SATIR is based on the heat transient method and is used as an inspection tool in order to assess component heat transfer capability. SATIR tests were performed on fingers integrating or not the complex He cooling system (steel cartridge with jet holes). Millimeter size artificial defects were manufactured and their detectability was evaluated. Results of this study demonstrate that the SATIR method can be considered as a relevant non-destructive technique examination for the defect detection of DEMO divertor fingers. 相似文献
53.
Luigi Brugnano Felice Iavernaro Donato Trigiante 《Computer Physics Communications》2012,183(9):1860-1868
We introduce a family of fourth-order two-step methods that preserve the energy function of canonical polynomial Hamiltonian systems. As is the case with linear mutistep and one-leg methods, a prerogative of the new formulae is that the associated nonlinear systems to be solved at each step of the integration procedure have the very same dimension of the underlying continuous problem.The key tools in the new methods are the line integral associated with a conservative vector field (such as the one defined by a Hamiltonian dynamical system) and its discretization obtained by the aid of a quadrature formula. Energy conservation is equivalent to the requirement that the quadrature is exact, which turns out to be always the case in the event that the Hamiltonian function is a polynomial and the degree of precision of the quadrature formula is high enough. The non-polynomial case is also discussed and a number of test problems are finally presented in order to compare the behavior of the new methods to the theoretical results. 相似文献
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55.
Algorithm transformation methods to reduce the overhead of software-based fault tolerance techniques
José Rodrigo Azambuja Gustavo Brown Fernanda Lima Kastensmidt Luigi Carro 《Microelectronics Reliability》2014
This paper introduces a framework that tackles the costs in area and energy consumed by methodologies like spatial or temporal redundancy with a different approach: given an algorithm, we find a transformation in which part of the computation involved is transformed into memory accesses. The precomputed data stored in memory can be protected then by applying traditional and well established ECC algorithms to provide fault tolerant hardware designs. At the same time, the transformation increases the performance of the system by reducing its execution time, which is then used by customized software-based fault tolerant techniques to protect the system without any degradation when compared to its original form. Application of this technique to key algorithms in a MP3 player, combined with a fault injection campaign, show that this approach increases fault tolerance up to 92%, without any performance degradation. 相似文献
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57.
Lorenzo Spinelli Giovanna Tissoni Luigi A. Lugiato Massimo Brambilla 《Journal of Modern Optics》2013,60(14-15):2413-2422
We introduce here a model which includes the thermal dynamics in the time evolution of a semiconductor multiple quantum well microresonator, driven by a coherent holding beam. The active layer is electrically pumped, in order to obtain population inversion, but it is maintained below the lasing threshold. We show that the inclusion of thermal effects introduces a Hopf instability which may dominate the dynamical behaviour of the system in some operational regimes. In those cases our numerical simulations show that both spatial patterns and cavity solitons perform a drift motion in the transverse direction. This motion develops over the slow time scale which characterizes thermal effects. 相似文献
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59.
Tania Martellini Chiara Berlangieri Luigi Dei Emiliano Carretti Saul Santini Angelica Barone Alessandra Cincinelli 《Indoor air》2020,30(5):900-913
Indoor Air Quality monitoring in cultural institutions is of particular concern to protect these places and the cultural heritage content. An indoor monitoring campaign was performed in three museums in Florence (Italy) to determine the occurrence and levels of volatile organic compounds (VOCs). VOCs of interest included BTEX (benzene, toluene, ethylbenzene, xylenes), terpenes, aldehydes, organic acids, and cyclic volatile methyl siloxanes (cVMS). The most abundant VOCs in all samples analyzed were BTEX, which were strictly related to the traffic source, followed by siloxanes and terpenes. Among BTEX, toluene was always the most abundant followed by xylenes, ethylbenzene, and benzene. cVMS in exhibition rooms with the presence of visitors showed higher values compared to samples collected when the museums were closed. Terpenes showed not only the influence of vegetation-biogenic sources surrounding a museum but could also be related to the wood used for the construction of showcases and furniture and the use of cleaning products. Data obtained also showed the presence of organic acids and aldehydes whose source can be traced back to exhibits themselves and wood-based furniture. Assessing the levels of organic acids in museums is important because, over time, it can cause deterioration of the artifacts. 相似文献
60.
Federico Bianchi Simone Formentin Luigi Piroddi 《International Journal of Adaptive Control and Signal Processing》2020,34(1):63-76
Kalman filtering for linear systems is known to provide the minimum variance estimation error, under the assumption that the model dynamics is known. While many system identification tools are available for computing the system matrices from experimental data, estimating the statistics of the output and process noises is still an open problem. Correlation-based approaches are very fast and sufficiently accurate, but there are typically restrictions on the number of noise covariance elements that can be estimated. On the other hand, maximum likelihood methods estimate all elements with high accuracy, but they are computationally expensive, and they require the use of external optimization solvers. In this paper, we propose an alternative solution, tailored for process noise covariance estimation and based on stochastic approximation and gradient-free optimization, that provides a good trade-off in terms of performance and computational load, and is also easy to implement. The effectiveness of the method as compared to the state of the art is shown on a number of recently proposed benchmark examples. 相似文献