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排序方式: 共有84条查询结果,搜索用时 250 毫秒
31.
Mazen Garaleh Mohammed Lahcini Hans R. Kricheldorf Steffen M. Weidner 《Journal of polymer science. Part A, Polymer chemistry》2009,47(1):170-177
Polycondensations of 1,6‐hexane diol and sebacic acid were conducted in bulk with addition of a lanthanide triflate as acidic catalyst. With exception of promethium triflate all lanthanide triflates were studied. A particularly low molecular weight was obtained with neodym triflate and the best results with samarium triflate. With Sm(OTf)3 weight average (Mw) values up to 65 kDa (uncorrected SEC data) were achieved after optimization of the reaction conditions. Comparison of these results with those obtained from bismuth, magnesium, and zinc triflates, on the one hand, and comparison with the acidities of all catalysts, on the other, indicates that the esterification mechanism involves complexation of monomer by metal ions. Preparation of multiblock copoly(ether ester)s failed due to insufficient incorporation of poly(tetrahydrofuran) diols. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 170–177, 2009 相似文献
32.
This paper gives a general convergence analysis to the truncated incomplete Hessian Newton method (T-IHN). It shows that T-IHN
is globally convergent even with an indefinite incomplete Hessian matrix or an indefinite preconditioner, which may happen
in practice. It also proves that when the T-IHN iterates are close enough to a minimum point, T-IHN has a Q-linear rate of
convergence, and an admissible line search steplength of one. Moreover, a particular T-IHN algorithm is constructed for minimizing
a biomolecular potential energy function, and numerically tested for a protein model problem based on a widely used molecular
simulation package, CHARMM. Numerical results confirm the theoretical results, and demonstrate that T-IHN can have a better
performance (in terms of computer CPU time) than most CHARMM minimizers. 相似文献
33.
The present paper deals with the theoretical modeling of symmetrical multilayer planar waveguide structure. One of the layers is considered as a negative refractive index material. We take the appropriate field distributions for p-polarization and impose the boundary conditions to derive the mode equation and other necessary formulae for the proposed structure. The effect of the negative-index layer on the modal refractive index, power flow, and penetration depth of the waveguide is studied. Also, we compare our computed results with those obtained for a similar conventional four-layer structure. It is observed that the presence of the negative-index material reduces the power flowing in the guiding layer and enhances the power flowing in the surroundings. 相似文献
34.
Mazen Bou Khuzam 《Journal of Geometry》2011,102(1-2):19-25
We present a comparative study of two fundamental invariants of exotic ${\mathbb R^{4}}$ ??s. The first invariant e(R) is defined intrinsically using the smooth compact submanifolds of R while the other ??(R) depends of the possibility of embedding R in some spin manifolds. We prove that ?? is dominated by e on all exotic ${\mathbb R^{4}}$ ??s. 相似文献
35.
Boris Andreianov Mazen Saad 《Journal of Computational and Applied Mathematics》2011,235(14):4015-4031
A finite volume method for solving the degenerate chemotaxis model is presented, along with numerical examples. This model consists of a degenerate parabolic convection-diffusion PDE for the density of the cell-population coupled to a parabolic PDE for the chemoattractant concentration. It is shown that discrete solutions exist, and the scheme converges. 相似文献
36.
A positive cell vertex Godunov scheme for a Beeler–Reuter based model of cardiac electrical activity
Mostafa Bendahmane Fatima Mroue Mazen Saad 《Numerical Methods for Partial Differential Equations》2021,37(1):262-301
The monodomain model is a widely used model in electrocardiology to simulate the propagation of electrical potential in the myocardium. In this paper, we investigate a positive nonlinear control volume finite element scheme, based on Godunov's flux approximation of the diffusion term, for the monodomain model coupled to a physiological ionic model (the Beeler–Reuter model) and using an anisotropic diffusion tensor. In this scheme, degrees of freedom are assigned to vertices of a primal triangular mesh, as in conforming finite element methods. The diffusion term which involves an anisotropic tensor is discretized on a dual mesh using the diffusion fluxes provided by the conforming finite element reconstruction on the primal mesh and the other terms are discretized by means of an upwind finite volume method on the dual mesh. The scheme ensures the validity of the discrete maximum principle without any restriction on the transmissibility coefficients. By using a compactness argument, we obtain the convergence of the discrete solution and as a consequence, we get the existence of a weak solution of the original model. Finally, we illustrate by numerical simulations that the proposed scheme successfully removes nonphysical oscillations in the propagation of the wavefront and maintains conduction velocity close to physiological values. 相似文献
37.
Neel A. Mansukhani Erica B. Peters Miranda M. So Mazen S. Albaghdadi Zheng Wang Mark R. Karver Tristan D. Clemons Jeffrey P. Laux Nick D. Tsihlis Samuel I. Stupp Melina R. Kibbe 《Macromolecular bioscience》2019,19(6)
The rising prevalence of cardiovascular disease worldwide necessitates novel therapeutic approaches to manage atherosclerosis. Intravenously administered nanostructures are a promising noninvasive approach to deliver therapeutics that reduce plaque burden. The drug liver X receptor agonist GW3965 (LXR) can reduce atherosclerosis by promoting cholesterol efflux from plaque but causes liver toxicity when administered systemically at effective doses, thus preventing its clinical use. The ability of peptide amphiphile nanofibers containing apolipoprotein A1–derived targeting peptide 4F to serve as nanocarriers for LXR delivery (ApoA1‐LXR PA) in vivo is investigated here. These nanostructures are found to successfully target atherosclerotic lesions in a mouse model within 24 h of injection. After 8 weeks of intravenous administration, the nanostructures significantly reduce plaque burden in both male and female mice to a similar extent as LXR alone in comparison to saline‐treated controls. Furthermore, they do not cause increased liver toxicity in comparison to LXR treatments, which may be related to more controlled release by the nanostructure. These findings demonstrate the potential of supramolecular nanostructures as safe, effective drug nanocarriers to manage atherosclerosis. 相似文献
38.
Nadine Allendörfer Mazen Es-Sayed Martin Nieger Stefan Bräse 《Tetrahedron letters》2012,53(4):388-391
Organofluorine compounds are of high interest in modern drug discovery and material sciences. We herein report a new synthetic access to o-amino-2,2,2-trifluoroacetophenones starting from commercially available o-amino benzoic acids, which can easily be converted into the corresponding benzoxazinones. In a second step the trifluoromethylated ketone is formed via addition of Ruppert’s reagent following acidic work up. 相似文献
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