Convergence analysis of a coupled method for time‐dependent convection‐diffusion equations

The coupling of two locally mass conservative methods is formulated and analyzed for the time‐dependent convection‐diffusion problem. Finite volume method is used in some subdomains and interior penalty discontinuous Galerkin method is used in other subdomains. Numerical examples show the advantages of the proposed hybrid method, namely an accurate approximation obtained at a reduced computational cost. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 133–157, 2014     

A full dimensional grid empowered simulation of the CO2 + CO2 processes

A recently introduced bond–bond formulation of the intermolecular interaction has been extended to six‐atom systems to the end of assembling a new potential energy surface (PES) and has been incorporated into a grid empowered simulator able to handle the modeling of the CO₂ + CO₂ processes. The proposed PES is full dimensional and accounts for the dependence of the intermolecular interaction on some basic physical properties of the colliding partners, including modulations induced by the monomer deformation. The used analytical formulation of the interaction involves a limited number of parameters, each having a clear physical meaning. Guess values for these parameters can also be obtained from analytical correlation formulae. Such estimates can then be fine tuned by exploiting experimental and theoretical information. The resulting PES well describes stretched and bent asymptotic CO₂ monomers as well as the CO₂–CO₂ interaction in the most and less stable configurations. On this potential massive quasiclassical elastic and inelastic detailed scattering trajectories have been integrated, by exploiting the innovative computational technologies of the grid. The efficiency of the approach used and the reliability of the estimates of the dynamical properties obtained in this way is such that we can now plan a systematic evaluation of the state specific rate coefficient matrix elements needed for space craft reentry modeling. Here, we present probabilities and cross sections useful to rationalize some typical mechanisms characterizing the vibrational transitions of the CO₂ + CO₂ system on the flexible monomer proposed PES. On such PES, the key dynamical outcomes are: (a) there is a strong energy interchange between symmetric stretching of the reactants and bending of the products (and viceversa) while asymmetric stretching is strongly adiabatic (b) reactant energy is more efficiently allocated (with respect to the rigid monomers PES) as product vibration when reactant stretching modes are excited while the contrary is true when the reactant bending mode is excited. © 2012 Wiley Periodicals, Inc.     

Surfactant-mediated desorption of polymer from the nanoparticle interface

The surfactant-mediated desorption of adsorbed poly(vinylpyrrolidone), PVP, from anionic silica surfaces by sodium dodecyl sulfate, SDS, was observed. While photon correlation spectroscopy shows that the size of the polymer-surfactant-particle ensemble grows with added SDS, a reduction in the near-surface polymer concentration is measured by solvent relaxation NMR. Volume fraction profiles of the polymer layer extracted from small-angle neutron scattering experiments illustrate that the adsorbed polymer layer has become more diffuse and the polymer chains more elongated as a result of the addition of SDS. The total adsorbed amount is shown to decrease due to Coulombic repulsion between the surfactant-polymer complexes and between the complexes and the anionic silica surface.     

Strong convergence of the discontinuous Galerkin scheme for the low regularity miscible displacement equations

Strong convergence of the numerical solution to a weak solution is proved for a nonlinear coupled flow and transport problem arising in porous media. The method combines a mixed finite element method for the pressure and velocity with an interior penalty discontinuous Galerkin method in space for the concentration. Using functional tools specific to broken Sobolev spaces, the convergence of the broken gradient of the numerical concentration to the weak solution is obtained in the L² norm. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 489–513, 2017     

Electron impact mass spectrometry of some geminal bis-sulphones

The behaviour under electron impact of six 1,1-bis(benzenesulphonyl)cyclioalkanes and of 1-phenyl-1-(benzensesulphaonyl)cyclopropane has been studied in detail with the aid of exact mass measurements, linked scans for metastable ion analysis, collisional spectroscopy and kinetic energy release measurements. The molecular ions of these compounds undergo a sulphone-sulphinate rearrangement with alkyl group migration on oxygen, in analogy with what is found for simple monosulphones and, in general, their fragmentation resembles that of mono-sulphonyl compounds. Loss of SO₂ from the molecular ion is observed for all substrates, but only in the case of 1, 1-bis(benzenesulphonyl)cyclopropane is this followed by loss of the second SO₂ unit; the first loss of SO₂ is probably accompanied by rearrangement since the fragmentation pattern of [M ? SO₂]⁺˙ ions from this compound is different than that of the isobaric molecular ions of 1-phenyl-1-(benzenesulphonyl)cyclopropane.     

Wave packet dynamics of H2(v1=8-14)+H2(v2=0-2): the role of the potential energy surface on different reactive and dissociative processes

A time-dependent wave packet method has been used to study different competing products of H(2)+H(2) collisions: four center reaction, collision induced dissociation, reactive dissociation, and three-body complex formation. A three-degree-of-freedom reduced dimensionality model has been used for five different geometries of the colliding complex (parallel H, crossed X, collinear L, and two T-shaped geometries T(I) and T(II)), with reactants in selected vibrational states with one diatom vibrationally "hot" and the other one vibrationally "cold." Product probabilities have been calculated using two potential energy surfaces [J. Chem. Phys. 101, 4004 (1994); J. Chem. Phys. 116, 666 (2002)] in order to compare their performance in the dynamics. The regions of the potential energy surfaces responsible of the threshold behavior of the probabilities have been identified. Overall, we have found that the most recent potential energy surface is less anisotropic, provides a smaller propensity for insertion-type processes, and gives lower energy thresholds.     

Monitoring the Evolution of Asynchrony between Mean Arterial Pressure and Mean Cerebral Blood Flow via Cross-Entropy Methods

Cerebrovascular control is carried out by multiple nonlinear mechanisms imposing a certain degree of coupling between mean arterial pressure (MAP) and mean cerebral blood flow (MCBF). We explored the ability of two nonlinear tools in the information domain, namely cross-approximate entropy (CApEn) and cross-sample entropy (CSampEn), to assess the degree of asynchrony between the spontaneous fluctuations of MAP and MCBF. CApEn and CSampEn were computed as a function of the translation time. The analysis was carried out in 23 subjects undergoing recordings at rest in supine position (REST) and during active standing (STAND), before and after surgical aortic valve replacement (SAVR). We found that at REST the degree of asynchrony raised, and the rate of increase in asynchrony with the translation time decreased after SAVR. These results are likely the consequence of the limited variability of MAP observed after surgery at REST, more than the consequence of a modified cerebrovascular control, given that the observed differences disappeared during STAND. CApEn and CSampEn can be utilized fruitfully in the context of the evaluation of cerebrovascular control via the noninvasive acquisition of the spontaneous MAP and MCBF variability.     

End‐group modified poly(methyl vinyl ether): Characterization and LCST demixing behavior in water

A range of hydrophilic poly(methyl vinyl ether) (PMVE) polymers was synthesized by living cationic polymerization of methyl vinyl ether (MVE), having different hydrophilic or hydrophobic chain‐end functionalities. The dissimilar end‐groups were either introduced by end‐capping of the growing polymer chain with LiBH₄, methanol, and water or by functional initiation with 2‐bromo‐(3,3‐diethoxy‐propyl)‐2‐methylpropanoate. The synthesized PMVEs were characterized by ¹H NMR, size exclusion chromatography, and matrix‐assisted laser desorption ionization time of flight, displaying a narrow polydispersity. Modulated temperature DSC was applied to study the influence of the nature of the end‐groups on the solubility behavior of PMVE in water. Terminal‐modification with a hydroxyl function improves the solubility, whereas a Br‐containing end‐group causes the polymer to be insoluble in water at room temperature; however, the special type III lower critical solution temperature demixing behavior being maintained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 461–469, 2006     

High-frequency properties of thin amorphous ribbons

Magnetic energy losses have been investigated in Co-based near-zero-magnetostriction amorphous ribbons from DC to 10 MHz. Attention has been devoted to the properties of field-annealed ribbons thinned down to 5.8 μm and their behavior at high frequencies. A rationale is provided for the frequency dependence of the magnetic losses over the investigated many-decade range through analysis of the loss components. Ribbons annealed under transverse field benefit by limited irreversible domain wall activity and correspondingly reduced hysteresis and excess losses. Based on the near-linear response of the material and the permeability–energy loss relationship, the separate contributions of domain wall displacements and rotations to the magnetization process and the related dissipation effects are singled out at all frequencies. Very thin amorphous ribbons are shown to display lower loss and higher permeability (i.e. higher Snoek's product) than Mn–Zn ferrites at all frequencies.     

Molecular-beam scattering and pressure broadening cross sections for the acetylene-neon system

Integral cross sections and pressure broadening coefficients have been measured for the acetylene — neon system by a molecular beam scattering technique and by high infrared resolution spectroscopy, respectively. We have performed quantal calculations using an ab-initio potential energy surface (PES) [J. Chem. Phys. 109, 8968 (1998)]. Results are found to be in good agreement with both measured integral cross sections and pressure broadening coefficients for the two temperatures investigated (173 and 298 K). We have also derived a semi-empirical PES parameterized using an atom-bond pairwise additive scheme. This PES shows an isotropic component in agreement with the ab-initio calculation, reproduces the scattering data but it only leads to a reasonable agreement for the pressure broadening coefficients.