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91.
Patrick Jenny Hamdi A. Tchelepi Seong H. Lee 《Journal of computational physics》2009,228(20):7497-7512
This paper addresses the convergence properties of implicit numerical solution algorithms for nonlinear hyperbolic transport problems. It is shown that the Newton–Raphson (NR) method converges for any time step size, if the flux function is convex, concave, or linear, which is, in general, the case for CFD problems. In some problems, e.g., multiphase flow in porous media, the nonlinear flux function is S-shaped (not uniformly convex or concave); as a result, a standard NR iteration can diverge for large time steps, even if an implicit discretization scheme is used to solve the nonlinear system of equations. In practice, when such convergence difficulties are encountered, the current time step is cut, previous iterations are discarded, a smaller time step size is tried, and the NR process is repeated. The criteria for time step cutting and selection are usually based on heuristics that limit the allowable change in the solution over a time step and/or NR iteration. Here, we propose a simple modification to the NR iteration scheme for conservation laws with S-shaped flux functions that converges for any time step size. The new scheme allows one to choose the time step size based on accuracy consideration only without worrying about the convergence behavior of the nonlinear solver. The proposed method can be implemented in an existing simulator, e.g., for CO2 sequestration or reservoir flow modeling, quite easily. The numerical analysis is confirmed with simulation studies using various test cases of nonlinear multiphase transport in porous media. The analysis and numerical experiments demonstrate that the modified scheme allows for the use of arbitrarily large time steps for this class of problems. 相似文献
92.
Jacques Darriet Hamdi Ben Yahia Etienne Gaudin 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(7):i79-i80
Single crystals of sodium tetracalcium trivanadium dodecaoxide were prepared by melting a powder sample of NaCa4(VO4)3 at 1673 K, followed by slow cooling to room temperature. The compound crystallizes in the Pnma space group and is isostructural with the mineral silicocarnotite, Ca5(PO4)2SiO4. The structure is composed of isolated VO4 tetrahedra linked by sodium and calcium cations disordered over eight‐ and seven‐coordinated sites. 相似文献
93.
Abdelwaheb Hamdi Young Hoon Lee Dewi K.A. Kusumahastuti Rym Abidi 《Tetrahedron letters》2009,50(5):540-551
The synthesis and complexation properties of a novel type of calix[4]azacrown, in which two cone calix[4]arenes are linked via a spiro C-atom incorporated into polyaminoalkylene chains are presented. 相似文献
94.
A new fluorogenic calix[4]tetraaza-crown-6 (4) bearing two pyrene amide groups has been prepared. It was shown to be selective for Mg2+. When Mg2+ is bound to 4, the pyrene monomer emission increased while the excimer emission declined in a ratiometric manner. It is shown by 1H NMR that this ratiometric change is due to the conformational changes of the pyrenes during the chelation of Mg2+ by the amide functions to form a 1:1 complex. 相似文献
95.
Regioselective 1,3‐dipolar cycloaddition of nitrilimines (generated in situ from dehydrohalogenation of the corresponding hydrazonoyl halides by the action of triethylamine) with 4‐arylidene‐1‐aryl‐2‐phenyl‐1H‐imidazol‐5(4H)‐one 3 afforded the corresponding spiro[4,4]nona‐2,8‐dien‐6‐one 4 . The reaction was carried out in dry benzene under reflux temperature. Refluxing in acetic acid, 4a was converted to its respective N‐phenylpyrazole‐5‐carboxamide 8 . The structures of prepared compounds were established by elemental analyses and spectral data (IR, MS, 1H, and 13C NMR). © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:131–136, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20666 相似文献
96.
Leuthold LA Mandscheff JF Fathi M Giroud C Augsburger M Varesio E Hopfgartner G 《Rapid communications in mass spectrometry : RCM》2006,20(2):103-110
Desorption electrospray ionization mass spectrometry (DESI-MS) was used as a simple and rapid way to analyze drug tablets and powders without sample preparation. Experiments were performed with a home-made DESI source coupled to a triple-quadrupole linear-ion trap (QqQ(LIT)) mass spectrometer. Twenty-one commercial drugs as well as some illicit Ecstasy tablets and powders were analyzed. MS spectra almost exclusively showed the protonated or deprotonated ion of the drug after directing the pneumatically assisted electrospray onto the tablet's surface. With some tablets, inhomogeneity of the surface resulted in different spectra depending on the spot analyzed, thus showing that DESI could be used for imaging. Directly triggered MS/MS spectra were used for confirmatory analysis, with analysis times often below 10 s per tablet. For illicit Ecstasy tablets, DESI-MS, GC/MS and LC/MS analyses provided similar qualitative results for the main analytes. With MS/MS spectra library comparison or exact mass measurements, this technique could become very powerful for the rapid analysis of unknown tablets and shows the great potential of desorption techniques as an alternative to solution-based analysis. 相似文献
97.
Production of natural fruity aroma by Geotrichum candidum 总被引:3,自引:0,他引:3
Mdaini N Gargouri M Hammami M Monser L Hamdi M 《Applied biochemistry and biotechnology》2006,128(3):227-235
Based on its aromatic potential, Geotrichum candidum isolated from olive vegetation water was tested for the production of volatile compounds. When G. candidum was cultivated on media with glucose as the carbon source, flavor volatile compounds were produced and accumulated in the
broth. Fruity flavoring compounds (pineapple-like) such as esters and alcohols were analyzed by gas chromatography coupled
to mass spectrometry, including ethyl esters of acetic acid and butyric acid, methyl-3-butan-1-ol, and methyl-2-propan-1-ol.
Their synthesis corresponded to the stationary growth phase of the strain. Production of the volatile compounds reached 9.5
g/L of 2-hexanoic acid ethyl ester and 1.6 g/L of benzaldehyde as the main concentrated molecules. Ethyl alcohol seems to
be an intermediate metabolite in this pathway. 相似文献
98.
Mohammad Mehdi Barzegari Morteza Dardel Alireza Fathi 《Acta Mechanica Solida Sinica》2013,26(5):536-550
In this study, analytical relations for evaluating the exact solution of natural fre- quency and mode shape of beams with embedded shape memory alloy (SMA) wires are presented. Beams are modeled according to Euler-Bernoulli, Timoshenko and third order beam (Reddy) the- ories. A relation is obtained for determining the effect of axial load generated by the recovery action of pre-strained SMA wires. By defining some dimensionless quantities~ the effect of different me- chanical properties on the frequencies and mode shapes of the system are carefully examined. The effect of axial load generated by SMA wires with buckling load and frequency jump is accurately studied. 相似文献
99.
The performance of the recently developed Link-Wise Artificial Compressibility Method (LW-ACM) is evaluated for aerodynamic applications and then applied for both attached and separated flows. Numerical flow simulations are performed around NACA-0012 and TSAGI-12 shaped airfoils at low speed and high angle of attack. Results of aerodynamic characteristics of the airfoils were found in good agreements with previous investigations including LBM (PowerFLOW) and FVM (CFL3D). Results also showed that LW-ACM is efficient and rapidly convergent when used to solve both attached and separated flows. 相似文献
100.
In a cancelable iris recognition technique, all enrollment patterns are masked using a transformation function, and the invertibility process for obtaining the original data should not be possible. A novel cancelable iris authentication approach in the encrypted domain is presented in this paper. The double random phase encoding (DRPE) algorithm in the Fractional Fourier Transform (FrFT) Domain is utilized to generate the optical masked IrisCodes. For the transmitter side, two encryption keys (RPM1 and RPM2) are utilized, while the second phase mask is proposed to be the right iris feature vector of the same user. As a result, mixing the feature vectors of the left and right iris patterns of the same subject to an encrypted IrisCode results in enhancing the privacy and preserving the system performance. This proposed system success is attributed to the fact that the iris authentication issue is transformed to a key authentication process. Experimental results conducted on CASIA-IrisV3-Interval dataset achieve a significant gain for both privacy and performance proving the superiority of the proposed approach. 相似文献