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排序方式: 共有264条查询结果,搜索用时 31 毫秒
31.
El Mostafa Daya Bouazza Braikat Noureddine Damil Michel Potier-Ferry 《Comptes Rendus Mecanique》2002,330(5):333-338
By homogenization theory, one can predict the vibrations of long repetitive structures in the low frequency range. Beyond this range, many modes have a modulated shape. Based on a multiple scale analysis, a continuum model is presented, that is able to account for this class of modes. This model involves a real coefficient that can be computed from the finite element resolution of problems defined on a few basic cells. An application in 2D elasticity is presented. To cite this article: E.M. Daya et al., C. R. Mecanique 330 (2002) 333–338. 相似文献
32.
In this study, the rachis extracts of eight date palm Phoenix dactylifera L. cultivars were analysed by phytochemical screening and bioautography on Fusarium oxysporum f. sp. albedinis (Foa). The choice of cultivars was based on their reaction to Foa (resistant, tolerant and sensitive). Phytochemical screening was realised for flavonoids, tannins, alkaloids and coumarins. Antifungal effects were mostly represented by dichloromethanic extracts (seven out of nine inhibition zones). The best results were represented by the dichloromethanic extract of the cultivar 'Bent-Cherk' rachis (6.50?±?1.41?mm) and the ethyl acetate extract of the cultivar 'Rotbi' rachis (6.00?±?1.41?mm). The date palm cultivars presented some similarities concerning phytochemical screening results related to their resistance or sensibility to Foa. From the correlation between phytochemical screening and bioautography, it was observed that the majority of bioactive compounds against Foa seem to be polyphenols. Thus, the natural defence mechanism in vivo against Foa is probably related to the action of polyphenols. The difference between resistant, tolerant and sensitive cultivars is related to their mechanism of action. 相似文献
33.
We propose a model that optimizes enterprise investments in cybersecurity using expected utility theory. The model allows computing (a) investment in self‐defense to reduce the risk of security breaches, (b) investment in cyber insurance to transfer the residual risk to insurance companies, and (c) investment in forensic readiness to make the insured firms capable of generating provable insurance claims about security breaches. A three‐phase–based model of vulnerability rate evolution over time is proposed and used to estimate the different planned security expenditures throughout the investment horizon. At the starting time of investment, a decision maker invests to cover the existing risk of breach and periodically spends to cover the additional risk observed due to the release of new vulnerabilities. In this work, the intermediate tranches are determined while considering three different attitudes of decision makers, namely, optimistic, pessimistic, and realistic. An analysis is conducted to assess the performance of the proposed models. 相似文献
34.
In this work, we intend to study the thermal
properties of the soaked steels like XC48 and their evolution according to
the heating temperature and for different soaking media, using the “Mirage
effect” method which permits the simultaneous determination of thermal
conductivity and diffusivity. We have observed a discontinuity of thermal
conductivity and diffusivity at the temperature of the ferro-paramagnetic
transition. 相似文献
35.
It is shown by construction that the only restriction on theintegral cohomology ring of a finitely presented asphericalgroup is that it has dimension at most 2. 相似文献
36.
An analytical method based on the modal expansion technique was developed to predict the vibro-acoustic response of both unidirectionally and bidirectionally stiffened flat panel. This paper presents the response to diffuse acoustic field (DAF) and turbulent boundary layer (TBL) excitations in terms of their joint acceptance. Numerical results for the dynamic and acoustic responses are compared with finite element method (FEM) and boundary element (BEM) results for stiffened panel with complex and eccentrically shaped stiffeners subject to point force excitation. A theoretical prediction of the transmission loss (TL) is also compared with laboratory measurements conducted on flat panels representing aircraft models as well as with hybrid statistical energy analysis (SEA)-FEM periodic model. The results confirm that the stiffened panel has the same acoustic response as the skin without stiffeners at frequencies where the structural wavelengths are equal to the spacing between the stiffeners. In addition, the transmission loss is lowered by the presence of the stiffeners at some particular region of frequencies below the critical frequency with respect to the unstiffened panel. 相似文献
37.
38.
Dazel O Sgard F Becot FX Atalla N 《The Journal of the Acoustical Society of America》2008,123(4):2054-2063
This paper is devoted to the rigorous obtention of the energy balance in porous materials. The wave propagation in the porous media is described by Biot-Allard's {u,U} and {u,P} formulations. The paper derives the expressions for stored kinetic and strain energies together with dissipated energies. It is shown that, in the case of mixed formulations, these expressions do not correspond to the real and imaginary parts of the variational formulations. A quantitative convergence analysis of finite element scheme is then undertaken with the help of these indicators. It is shown that the order of convergence of these indicators for linear finite-element is one and that they are then well fitted to check the validity of finite-element models. 相似文献
39.
Mehiaoui Nawel Kibou Zahira Berrichi Amina Bachir Redouane Choukchou-Braham Noureddine 《Research on Chemical Intermediates》2020,46(12):5263-5280
Research on Chemical Intermediates - The current work described a new and highly selective method for the synthesis of substituted 3-cyano-2-pyridones scaffolds using gold-cobalt supported on TiO2... 相似文献
40.
Eman Al-Abbad Alakhras Fadi Anastopoulos Ioannis Das Debashis AL-Arfaj Ahlam Ouerfelli Noureddine Hosseini-Bandegharaei Ahmad 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2020,94(4):748-755
Russian Journal of Physical Chemistry A - Sorption of Ni(II) ions from liquid effluents utilizing chemically modified chitosan; (vanillin, polymer I) and (ortho-vanillin, polymer II) is studied... 相似文献