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61.
Fabrice Rousselle Petrik Clarberg Luc Leblanc Victor Ostromoukhov Pierre Poulin 《The Visual computer》2008,24(7-9):465-474
We present an efficient method for importance sampling the product of multiple functions. Our algorithm computes a quick approximation of the product on the fly, based on hierarchical representations of the local maxima and averages of the individual terms. Samples are generated by exploiting the hierarchical properties of many low-discrepancy sequences, and thresholded against the estimated product. We evaluate direct illumination by sampling the triple product of environment map lighting, surface reflectance, and a visibility function estimated per pixel. Our results show considerable noise reduction compared to existing state-of-the-art methods using only the product of lighting and BRDF. 相似文献
62.
Search games are attractive for their correspondence with classical width parameters. For instance, the invisible search number (a.k.a. node search number) of a graph is equal to its pathwidth plus 1, and the visible search number of a graph is equal to its treewidth plus 1. The connected variants of these games ask for search strategies that are connected, i.e., at every step of the strategy, the searched part of the graph induces a connected subgraph. We focus on monotone search strategies, i.e., strategies for which every node is searched exactly once. The monotone connected visible search number of an n-node graph is at most O(logn) times its visible search number. First, we prove that this logarithmic bound is tight. Precisely, we prove that there is an infinite family of graphs for which the ratio monotone connected visible search number over visible search number is Ω(logn). Second, we prove that, as opposed to the non-connected variant of visible graph searching, “recontamination helps” for connected visible search. Precisely, we prove that, for any k4, there exists a graph with connected visible search number at most k, and monotone connected visible search number >k 相似文献
63.
This paper introduces time stream Pétri nets (Ts treamPn), a model for the formal specification of multimedia synchronization scenarios. This new model extends time Pétri nets to formally describe the timed behaviour of multimedia objects and streams in asynchronous distributed systems. The proposed approach uses time intervals to label the arcs exiting from the places of the net, and typed transitions to define different firing rules. This model allows a complete and accurate specification of synchronization constraints between multimedia streams and can be used at different levels of granularity. 相似文献
64.
Pierre Lescanne 《Formal Aspects of Computing》1995,7(1):77-90
We focus on termination proofs of rewrite systems, especially of rewrite systems containing associative and commutative operators. We prove their termination by elementary interpretations, more specifically, by functions defined by addition, multiplication and exponentiation. We discuss a method based on polynomial interpretations and propose an implementation of a mechanisation of the comparison of expressions built with polynomials and exponentials. 相似文献
65.
Chapellier Paul Lavenus Pierre Le Traon Olivier Dulmet Bernard 《Microsystem Technologies》2022,28(6):1485-1496
Microsystem Technologies - This paper presents recent advances on two dimensional length-extension mode (2D-LEM) quartz resonators providing high quality (Q) factor on resonances at a few MHz. The... 相似文献
66.
67.
We investigate the ability to move of large objects—referred to as intruders—embedded in a granular material and subjected to cyclic loadings. A discrete element method is used to simulate the dynamics response of intruders subjected to a vertical uplift cyclic force, exploring a wide range of loading magnitudes and frequencies. The analysis of the intruder and grains displacements over many cycles reveals three mobility regimes. In the first two regimes, called confined and failure the intruder either do not significantly move or consistently moves upward after each cycles. We introduce a physically based model considering an inertial drag force to rationalise the existence of these regimes depending on the loading frequency and magnitude. We further evidence a third intermediate regime of creep, where intruder trajectories exhibit long periods of confinement punctuated by shorter periods of sustained uplift motion. Finally, we observe unexpected failures at low loading magnitudes and specific frequencies, which we attribute to a process of elasto-inertial resonance. These results highlight the important differences in the mobility of intruders upon constant and cyclic loadings. 相似文献
68.
Oxidative Stress Imaging: Visualizing Oxidative Cellular Stress Induced by Nanoparticles in the Subcytotoxic Range Using Fluorescence Lifetime Imaging (Small 23/2018) 下载免费PDF全文
69.
Malte Krack Marc Secanell Pierre Mertiny 《Structural and Multidisciplinary Optimization》2011,44(1):57-73
A procedure to find the optimal design of a flywheel with a split-type hub is presented. Since cost plays a decisive role
in stationary flywheel energy storage applications, a trade-off between energy and cost is required. Applying a scaling technique,
the multi-objective design problem is reduced to the maximization of the energy-per-cost ratio as the single objective. Both
an analytical and a finite element model were studied. The latter was found to be more than three orders of magnitude more
computationally expensive than the analytical model, while the analytical model can only be regarded as a coarse approximation.
Multifidelity approaches were examined to reduce the computational expense while retaining the high accuracy and large modeling
depth of the finite element model. Using a surrogate-based optimization strategy, the computational cost was reduced to only
one third in comparison to using only the finite element model. A nonlinear interior-point method was employed to find the
optimal rim thicknesses and rotational speed. The benefits of the split-type hub architecture were demonstrated. 相似文献
70.
Omnibus procedures for testing serial correlation are developed, using spectral density estimation and wavelet shrinkage. The asymptotic distributions of the wavelet coefficients under the null hypothesis of no serial correlation are derived. Under some general conditions on the wavelet basis, the wavelet coefficients asymptotically follow a normal distribution. Furthermore, they are asymptotically uncorrelated. Adopting a spectral approach and using results on wavelet shrinkage, new one-sided test statistics are proposed. As a spatially adaptive estimation method, wavelets can effectively detect fine features in the spectral density, such as sharp peaks and high frequency alternations. Using an appropriate thresholding parameter, shrinkage rules are applied to the empirical wavelet coefficients, resulting in a non-linear wavelet-based spectral density estimator. Consequently, the advocated approach avoids the need to select the finest scale J, since the noise in the wavelet coefficients is naturally suppressed. Simple data-dependent threshold parameters are also considered. In general, the convergence of the spectral test statistics toward their respective asymptotic distributions appears to be relatively slow. In view of that, Monte Carlo methods are investigated. In a small simulation study, several spectral test statistics are compared, with respect to level and power, including versions of these test statistics using Monte Carlo simulations. 相似文献