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排序方式: 共有86条查询结果,搜索用时 60 毫秒
1.
Luis C. Mendes Andrea D. Tedesco Mauro S. Miranda Marcia R. Benzi Beatriz S. Chagas 《Polymer Testing》2005,24(8):963-968
In this third work, we evaluated the degree of conversion (DC) versus depth of dental filling composite named Prodigy Condensable™ using infrared spectroscopy. Confirming previous results, there was a gradual reduction of DC with increasing depth but the composite exhibited extreme values of DC, an upper value (45.9%) on the surface and a lower one (6.1%) at a depth of 5 mm. The composite presented the worst performance among materials studied. The composite formulation was 80% of inorganic fillers and BisfenolA/dimethacrylate (BisGMA) (18%)/triethyleneglycoldimethacrylate (TEGDMA) (2.0%) as monomers. As stated before, type/ratio/viscosity of monomers and type, amount, size and size distribution of fillers all together had an important role in the cure reaction contributing to the final performance of the composite. 相似文献
2.
Improta R Mele F Crescenzi O Benzi C Barone V 《Journal of the American Chemical Society》2002,124(26):7857-7865
The importance of vicinal and long-range interresidue effects in determining the stability of the collagen triple helix has been investigated by quantum mechanical (QM) and molecular mechanical (MM) computations on suitable model polypeptides, taking into account solvent effects by the polarizable continuum model (PCM). At the QM level, the PII conformation corresponds to an energy minimum for pentapeptide analogues incorporating the sequence Gly-Pro-Pro-Gly, irrespective of the down or up puckering of the pyrrolidine ring. However, our computations indicate that the alternation of down and up prolines characterizing collagen and collagen-like peptides is not due to an intrinsic preference of the Pro-Pro-Gly sequence. This result is confirmed by MM computations of longer polypeptides. Next, MM computations on model triple helices show that a better packing is obtained for specific values of backbone dihedrals, which, in turn, favor the alternation of down and up prolines along each chain. 相似文献
3.
BIT Numerical Mathematics - In this paper we propose a method to compute the solution to the fractional diffusion equation on directed networks, which can be expressed in terms of the graph... 相似文献
4.
The conformational behavior of the title compounds has been investigated by Hartree-Fock, MP2, and DFT computations on the most significant structures related to variations of the backbone dihedral angles, cis/trans isomerism around the peptide bond, and diastereoisomeric puckering of the pyrrolidine ring. In vacuum the reversed gamma turn (gammal), characterized by an intramolecular hydrogen bridge, corresponds to the absolute energy minimum for both puckerings (up and down) of the pyrrolidine ring. An additional energy minimum is found in the helix region, but only for an up puckering of the pyrrolidine ring. When solvent effects are included by means of the polarizable continuum model the conformer observed experimentally in condensed phases becomes the absolute minimum. The down puckering is always favored over its up counterpart, albeit by different amounts (0.4-0.5 kcal/mol for helical structures and about 2 kcal/mol for gammal structures). In helical structures cis arrangements of the peptide bond are only slightly less stable than their trans counterparts. This is no longer true for gammal structures, because the formation of an intramolecular hydrogen bond is possible only for trans peptide bonds. In most cases, proline and hydroxyproline show the same general trends; however, the electronegative 4(R) substituent of hydroxyproline leads to a strong preference for up puckerings irrespective of the backbone conformation. 相似文献
5.
6.
We describe a parallel implementation of a block triangular preconditioner based on the modified augmented Lagrangian approach to the steady incompressible Navier–Stokes equations. The equations are linearized by Picard iteration and discretized with various finite element and finite difference schemes on two- and three-dimensional domains. We report strong scalability results for up to 64 cores. 相似文献
7.
8.
Drag reduction by polymers in wall turbulence is bounded from above by a universal maximal drag reduction (MDR) velocity profile that is a log law, estimated experimentally by Virk as V+(y+) approximately 11.7logy+ - 17. Here V+(y+) and y+ are the mean streamwise velocity and the distance from the wall in "wall" units. In this Letter we propose that this MDR profile is an edge solution of the Navier-Stokes equations (with an effective viscosity profile) beyond which no turbulent solutions exist. This insight rationalizes the universality of the MDR and provides a maximum principle which allows an ab initio calculation of the parameters in this law without any viscoelastic experimental input. 相似文献
9.
Paola Benzi Elena Bottizzo Chiara Demaria Nicoletta Rizzi 《Journal of Chemical Sciences》2007,119(6):631-635
YBa2Cu3Ox (Y-123) and Bi2Sr2Ca1Cu2Ox (Bi-2212) films on various substrates have been prepared by Metal-Organic Deposition starting from different metallorganic
fluorine-free compounds and using a very simple instrumentation. The processing conditions include a rapid pyrolysis step
in air and an annealing step in oxygen for Y-123 and in air for Bi-2212. The films obtained have been characterized by X-ray
diffraction (XRD) and the formation of a superconducting phase of Y-123 or Bi-2212 was confirmed measuring the critical temperature
(T
c) with Ac-susceptibility and resistive measurements. Microstructure and final cationic ratios have been studied by scanning
electron microscopy (SEM) and energy dispersive spectroscopy (EDS). 相似文献
10.
Michele Benzi Eldad Haber Lauren Taralli 《Advances in Computational Mathematics》2011,35(2-4):149-173
We investigate the use of a preconditioning technique for solving linear systems of saddle point type arising from the application of an inexact Gauss?CNewton scheme to PDE-constrained optimization problems with a hyperbolic constraint. The preconditioner is of block triangular form and involves diagonal perturbations of the (approximate) Hessian to insure nonsingularity and an approximate Schur complement. We establish some properties of the preconditioned saddle point systems and we present the results of numerical experiments illustrating the performance of the preconditioner on a model problem motivated by image registration. 相似文献