Refining the submesh strategy in the two‐level finite element method: application to the advection–diffusion equation

We introduce a new submesh strategy for the two‐level finite element method. The numerical results show that the new submesh is able to better capture the boundary layer which is caused by the choice of bubble functions. The effect of an improved approximation of the residual free bubbles is studied for the advective–diffusive equation. Copyright © 2002 John Wiley & Sons, Ltd.     

Comparison of partial digestion procedures for determination of Ca, Cr, Cu, Fe, K, Mg, Mn, Na, P, and Zn in milk by inductively coupled plasma-optical emission spectrometry

A fast procedure was developed for determination of Ca, Cr, Cu, Fe, K, Mg, Mn, Na, P, and Zn in milk samples. This procedure consisted of a partial digestion with hydrochloric acid on a hot plate. The results obtained were compared with 3 other digestion procedures (dry ashing and 2 microwave digestions). All the procedures showed similar precision levels, with coefficients of variation <10% for most analyzed elements. Accuracy was evaluated by using certified reference materials, and the values obtained were within the confidence intervals for these products. The results obtained were not considered statistically different. The partial digestion on a hot plate with HCl can be very practical for laboratories with relatively large numbers of sample analyses.     

Synthesis and Structural Characterisation of Two Novel Diastereoisomeric Naproxen Appended β-Cyclodextrin Derivatives

The condensation reaction of 6-deoxy-6-amino(2-aminoethyl)-cyclomaltoheptaose (β-CyDen) and racemic [(R, S)-2-(6-methoxy-2-naphthyl) propanoic acid] (R,S-naproxen) affords two new diastereoisomeric naproxen-appended β-cyclodextrin derivatives. The structural analysis of these two β-CyD derivatives, undertaken by combined use of circular dichroism (CD) and 1D or 2D NMR techniques, shows that the naphthalene ring of the naproxen is included in the CyD cavity in both derivatives. The CD spectra are consistent with an axial complexation model, moreover, the self-inclusion mode is further corroborated by ¹H NMR ROESY spectra which also suggest the orientation of the naphthyl moiety in the cavity of both the diastereoisomers.     

Enantioselective total synthesis of (1R,3S,4R,5R)-1-amino-4,5-dihydroxycyclopentane-1,3-dicarboxylic acid. A full-aldol access to carbaketose derivatives

The enantioselective synthesis of cyclopentanedicarboxylic amino acid 1, a novel rigid and functionalized L-glutamic acid analogue, has been achieved in 15 linear steps from silyloxypyrrole 3, utilizing L-glyceraldehyde 4 as the source of chirality. The key steps in the synthesis are three sequential aldol-based carbon-carbon bond-forming reactions: two crossed vinylogous aldol additions (2 + 3 --> 8 and 4 + 5 --> 10 + 11) and one intramolecular silylative aldolization (6 --> 7). En passant, the short syntheses of (2S)-2-hydroxymethylglutamic acid (16) and its (2R)-enantiomer ent-16, a potent metabotropic glutamate receptor agonist, have been achieved.     

Stability and cations coordination of DNA and RNA 14-mer G-quadruplexes: a multiscale computational approach

Molecular dynamics simulations have been used to study the differences between two DNA and RNA 14-mer quadruplexes of analogous sequences. Their structures present a completely different fold: DNA forms a bimolecular quadruplex containing antiparallel strands and diagonal loops; RNA forms an intrastrand parallel quadruplex containing a G-tetrad and an hexad, which dimerizes by hexad stacking. We used a multiscale computational approach combining classical Molecular dynamics simulations and density functional theory calculations to elucidate the difference in stability of the 2-folds and their ability in coordinating cations. The presence of 2'-OH groups in the RNA promotes the formation of a large number of intramolecular hydrogen bonds that account for the difference in fold and stability of the two 14-mers. We observe that the adenines in the RNA quadruplex play a key role in conserving the geometry of the hexad. We predict the cation coordination mode of the two quadruplexes, not yet observed experimentally, and we offer a rationale for the corresponding binding energies involved.     

Vicarious silylative Mukaiyama aldol reaction: a vinylogous extension

A vinylogous, silylative, and direct variant of the venerable Mukaiyama aldol reaction has been developed. Exploiting N-Boc-pyrrol-2(5H)-one as the conjugate donor, several aldehyde and ketone acceptors were scrutinized under the guidance of suitable dual Lewis acid-Lewis base activators to provide a varied repertoire of functionality-rich alpha,beta-unsaturated-gamma-amino-delta-silyloxy carbonyl structures, in useful yields and often with an exquisite level of diastereoselection.     

Mathematical models for the non‐isothermal Johnson–Segalman viscoelasticity in porous media: stability and wave propagation

We present a nonlinear model for Johnson–Segalman type polymeric fluids in porous media, accounting for thermal effects of Oldroyd‐B type. We provide a thermodynamic development of the Darcy's theory, which is consistent with the interlacement between thermal and viscoelastic relaxation effects and diffusion phenomena. The appropriate invariant convected time derivative for the flux vector and the stress tensor is discussed. This is performed by investigating the local balance laws and entropy inequality in the spatial configuration, within the single‐fluid approach. For constant parameters, our thermomechanical setting is of Jeffreys type with two delay time parameters, and hence, in the linear/linearized version, it is strictly related to phase‐lag theories within first‐order Taylor approximations. A detailed spectral analysis is carried out for the linearized version of the model, with a scrutiny to some significant limit situations, enhancing the stabilizing effects of the dissipative and elastic mechanisms, also for retardation responses. For polymeric liquids, rheological aspects, wave propagation properties and analogies with other theories with lagging are pointed out. Copyright © 2014 John Wiley & Sons, Ltd.     

Continuous dependence on boundary and Soret coefficients in double diffusive bidispersive convection

We develop a theory for double diffusive convection in a double porosity material along the Brinkman scheme. The Soret effect is included whereby a temperature gradient may directly influence salt concentration. The boundary conditions on the temperature and salt fields are of general Robin type. A number of a priori estimates are established whereby, through energy arguments, we prove continuous dependence of the solution on the Soret coefficient and on the coefficients in the boundary conditions in the L²- norm.