Strong-stability-preserving 3-stage Hermite-Birkhoff time-discretization methods

Strong-stability-preserving (SSP) time-discretization methods have a nonlinear stability property that makes them particularly suitable for the integration of hyperbolic conservation laws. A collection of SSP explicit 3-stage Hermite-Birkhoff methods of orders 3 to 7 with nonnegative coefficients are constructed as k-step analogues of third-order Runge-Kutta methods, incorporating a function evaluation at two off-step points. Generally, these new methods have larger effective CFL coefficients than the hybrid methods of Huang with the same step number k. They have larger maximum scaled step sizes than hybrid methods on Burgers' equations.     

Effect of the Zn2+ and Hg2+ ions on the structure of liquid water

The effect of ions on the structure of liquid water is still not completely understood, despite extensive experimental and theoretical studies. A combined XANES and molecular dynamics investigation on diluted Zn(2+) and Hg(2+) aqueous solutions reveals that the influence of a single ion on the bonding pattern of water molecules is strongly dependent on the nature of the ion. While the structure of water is not altered by the presence of the Zn(2+) ion, the Hg(2+) cation has a strong impact on the hydrogen-bond network of water that extends beyond the first coordination shell.     

Review of Experimental Data on Incompressible Turbulent Round Jets

This article reviews measurements for the canonical flow: incompressible turbulent round jets issuing into a large, ideally infinite, quiescent domain. The available far-field data on mean velocity, momentum-flux conservation, Reynolds stresses and triple fluctuation correlations are presented. The budget equations for turbulent kinetic energy and for the individual Reynolds stresses are shown, including different formulations for dissipation and pressure-velocity correlations. Evidence of the persistence of source conditions in the self-preserving far field is observed in several cases. This article analyses and compares several data sets, obtained at different levels of detail, against analytical constraints, discusses limitations and provides insights aided by reference to recent numerical work. It is hoped that this will prove useful in guiding future experiments and numerical test cases, where complete details of the jet configuration are required for validation and comparison.     

Effect of the segmental mobility restriction on the thermoset chemical kinetics

The cure kinetics of an epoxy–amine commercial thermoset system have been investigated with the isothermal differential scanning calorimetry technique. In particular, a kinetic study has been performed in the glass–transition zone, in which diffusion phenomena compete with the chemical transformations and the overall reaction rate is partially slowed by the reduced segmental chain mobility. A generalized form of the Vogel equation has been formulated to account for the effect of the increasing glass–transition temperature on the chain mobility and, therefore, on the overall reaction rate. The kinetic model has been expressed with two factors representing the chemical reaction rate and the segmental mobility reduction. As the main result, the activation energy relative to the diffusion phenomena has been found to be very low, having a value of 42.5 K ≈ 0.356 kJ/mol, which is compatible only with the small‐angle rotation of the reactive unit. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3757–3770, 2002     

Dispersity effect of platinum supported on honeycomb carrier on its activity in benzene hydrogenation

Specific activity of Pt catalysts prepared by supporting Pt(-C₄H₇)₂ or H₂PtCl₆ on a honeycomb carrier in benzene hydrogenation in the kinetic region has been established to remain unchanged with increasing Pt particle size from 10 to 50 Å.

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, Pt(-C₄H₇)₂ H₂PtCl₆ , Pt 10Å 50Å.

     

Polar effects in free-radical reactions. New synthetic developments in the functionalization of heteroaromatic bases by nucleophilic radicals

The synthetic interest of the direct substitution of protonated heteroaromatic bases by nucleophilic carbon-centered radicals is furtheron developed by the following new achievements: i) utilization of the redoc system

in several solvents; ii) utilization of benzoyl peroxide in alcohols; iii) carbamoylation by HCONH₂ and H₂O₂ in the presence of catalytic amounts of Fe(II). These systems allow to obtain either substitution till now tried without success or reactions of industrial interest. Polar effects play a dominant role in determining reactivity, selectivity and synthetic applications; in particular the role of the strongly nucleophilic intermediate radicals of pyridinyl type in the rearomatization step is emphasized.     

Conductive cooling of magmatic intrusions: Short calculation models

Summary We propose some approximate, expedite models for calculating the conductive cooling of magmatic intrusions. At great depths, conduction can account for more cooling than convective phenomena, for tens of thousands of years. Numerical simulation of the thermal development of a region by explicit Euler method requires an appropriate proportion between the quantizations of time and space. Only thus can a numerical solution be obtained, which is consistent and stable, and which conforms to the second law of thermodynamics. In order to account for the geometry and volumetric limits of actual intrusions, we resorted to cylindrical representations rather than to the Cartesian ones used in the references Work conducted at the Naval University Institute of Naples under a 1985 grant from the Ministry of Public Education.