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排序方式: 共有306条查询结果,搜索用时 31 毫秒
21.
Alexander V. Avdeev Eldar V. Goriounov Mikhail M. Lavrentiev Jr. Renato Spigler 《Applied Mathematical Modelling》2009
A behavior-oriented diffusion model, governing the time evolution of the cross-shore position of coastal profiles, is studied. Here, two time-independent, space-varying coefficients, which embody the relevant physical properties, are identified simultaneously. Two sets of real data, the first measured over 10 years at Duck, in NC (USA), the second obtained over 39 years measurements at Delfland (Holland), have been processed numerically by a suitable “inversion algorithm”, earlier developed by the authors. This is based on the minimization of a certain cost functional in order to identify both coefficients. The numerical results, obtained by solving the diffusion equation with the so-determined coefficients, favorably agree with the real data, which fact validates and calibrates somehow the diffusion model under investigation. A short-term prediction is finally obtained for coastal profiles, using such a model. 相似文献
22.
The Kaczmarz method is an algorithm for finding the solution to an overdetermined consistent system of linear equations Ax = b by iteratively projecting onto the solution spaces. The randomized version put forth by Strohmer and Vershynin yields provably
exponential convergence in expectation, which for highly overdetermined systems even outperforms the conjugate gradient method.
In this article we present a modified version of the randomized Kaczmarz method which at each iteration selects the optimal
projection from a randomly chosen set, which in most cases significantly improves the convergence rate. We utilize a Johnson–Lindenstrauss
dimension reduction technique to keep the runtime on the same order as the original randomized version, adding only extra
preprocessing time. We present a series of empirical studies which demonstrate the remarkable acceleration in convergence
to the solution using this modified approach. 相似文献
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24.
Fatemeh Safdari Pierre J. Carreau Marie C. Heuzey Musa R. Kamal 《Cellulose (London, England)》2017,24(7):2877-2893
Polylactide (PLA)/cellulose nanofiber (CNF) biocomposites were prepared via solution casting and direct melt mixing. To improve the compatibility, a masterbatch of CNFs and poly(ethylene glycol) (PEG) (1:2) was also prepared. The effects of PEG on the morphology and properties of the biocomposites were investigated. The dispersion/distribution of nanofibers in PLA was improved when the masterbatch was used and the composites were prepared in solution. Substantial effects on the rheological properties of solution-prepared PLA/CNF/PEG composites were observed compared to composites containing no PEG, whereas for melt-prepared composites no significant changes were detected. Increased crystalline content and crystallization temperature were observed for the composites prepared via the masterbatch and solvent casting. The storage modulus of PLA was increased by 42 and 553% at 25 and at 80 °C, respectively, for the solution-based PEG-compatibilized composite containing 2 wt% nanofibers. Also, a better light transmittance was measured for the PLA/CNF/PEG composites prepared in solution. 相似文献
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26.
根据电镜断面考察结果,以Gurson模型为本构方程的有限单元
法对包体模型及三维非均匀模型进行了详细分析. 为了评价应力-应变
关系及损伤的主要因素,考虑了基体中SiC粒子的体积率和径比的非均
匀分布. 其结果表明,用这种非均匀模型能很好地仿真铝基体在大量塑
性变形之后所发生的韧窝破坏过程. SiC粒子体积率、径比及其位置的
非均匀性,对局部和整体损伤过程与应力-应变关系的影响相当大. 当
Sic粒子径比为1.0,并在基体中均匀分布时,断裂应变会大幅度增大. 相似文献
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29.
Hassan Keypour Musa AhmadiMajid Rezaeivala Abdolkarim ChehreganiReza Golbedaghi Allan G. Blackman 《Polyhedron》2011,30(11):1865-1870
Two new branched pentadentate amines (N5), 3,7-bis(2-pyridylmethyl)-5,5-dimethyl-3,7-diazaheptane-1-amine (1) and 4,8-bis(2-pyridylmethyl)-6,6-dimethyl-4,8-diaza octane-1-amine (2) have been prepared. These have been used to synthesis two new Schiff base complexes containing a pyridine and 2-pyridylmethyl pendant arm, by template [1+1] condensation of pyridine-2-carbaldehyde with the amines in the presence of Mn(II) in methanol. Elemental and spectral results are used to characterize the complexes and their structures are confirmed by single crystal X-ray diffraction studies. The structure of MnL1(ClO4)2 indicates that in the solid state the Mn(II) ion adopts a slightly distorted octahedral geometry. The crystal structure of [Ni(1)(MeCN)](ClO4)2 is also reported and exhibits a slightly distorted octahedral geometry. Also the synthesized complexes were screened for their antibacterial activity against Escherichia coli (Lio), Serratia marcescens (PTCC 1330), Staphylococcous aureus (ATCC 6633), and Proteus vulgaris (Lio) and results showed that the all complexes have antibacterial effects and [NiL1](ClO4)2, [MnL2](ClO4) and [MnL1](ClO4)2 have more effective ones against E. coli. 相似文献
30.
Seventeen compounds, including a new lanostane triterpenoid, 24(Z)-1β-3β-dihydroxyeupha-7,24-dien-26-oic acid, have been isolated from the methanolic extracts of two samples of Jordanian propolis collected from two different places with different dominant flora. The structures of the isolated compounds were elucidated by spectral methods including IR, UV, MS and 1- and 2-D NMR. 相似文献