A nonlocal convective flux limiter for upwind‐biased finite volume simulations

Finite volume methods on structured and unstructured meshes commonly use second‐order, upwind‐biased linear reconstruction schemes to approximate the convective terms. Limiters are employed to reduce the inherent variable overshoot and undershoot of these schemes in discontinuous regions; however, they also can significantly increase the numerical dissipation of a solution in smooth regions. This paper presents a novel nonlocal, nonmonotonic (NLNM) limiter developed by enforcing cell minima and maxima on dependent variable values projected to cell faces. The minimum and maximum values for a cell are determined primarily through recursive reference to the minimum and maximum values of its upwind neighbors. The new limiter has been implemented into an existing flow solver. Various test cases are presented, which highlight the ability of the NLNM limiter to eliminate nonphysical oscillations while maintaining negligible levels of limiter‐induced dissipation into the solution. Results from the new limiter are compared with those from other limited and unlimited second‐order upwind and first‐order upwind schemes. For the cases examined in the study, the NLNM limiter was found to improve accuracy without significantly decreasing overall simulation efficiency and robustness.Copyright © 2011 John Wiley & Sons, Ltd.     

De Réaumur à la Première Guerre Mondiale : les étapes de la maîtrise de l’acier,l’essor des aciers spéciaux

After a brief survey of the history of steel-making we shall concentrate on the period extending from Réaumur's work on that topic (1722) until World War one. Those two centuries saw the transition from empirical steel production processes to industrial steel manufacturing. We shall see how problems linked to the quenching and cementation of steel caused both scientists and steel manufacturers to develop efficient research leading to the establishment of an authentic metal science around 1900. These scientific discoveries then contributed to the prodigious development of special steel. Originally produced empirically to fulfill military requirements, these new types of material were to answer the needs of emerging industries, such as electrical engineering, as well as car manufacturing.     

Effect of composition on the short-term and long-term dissolution rates of ten borosilicate glasses of increasing complexity from 3 to 30 oxides

Ten borosilicate glass compositions consisting of a ternary sodium borosilicate containing increasing numbers of some of the key elements (Al, Ca, Zr, Ce) present in nuclear glasses were leached in pure water at 90 °C and monitored for up to 14 years. They were then characterized to establish correlations between the glass composition and the short- and long-term alteration rates. We first qualitatively explain the variations of the initial dissolution rate by structural considerations. Then we evidence a qualitative inverse correlation between the initial and residual rates. This counterintuitive result is in fact related to the effect of gel reorganization on the diffusive properties of the passivating layer. Since no equilibrium can be reached between glass and solution, these long-term experiments help in understanding how glasses behave once the solution is saturated with respect to the main glass formers. Very efficient synergy between Ca and hardener elements (Al or Zr) leads to the lowest residual rates, compared with glasses having only one of the two categories of elements. We also confirm the detrimental effect of precipitation of silicate minerals on the residual rate.     

Positive semidefinite zero forcing

The positive semidefinite zero forcing number _Z+(G)${\mathrm{Z}}_{+}(G)$ of a graph G was introduced in Barioli et al. (2010) [4]. We establish a variety of properties of _Z+(G)${\mathrm{Z}}_{+}(G)$: Any vertex of G   can be in a minimum positive semidefinite zero forcing set (this is not true for standard zero forcing). The graph parameters tw(G)$\mathrm{tw}(G)$ (tree-width), _Z+(G)${\mathrm{Z}}_{+}(G)$, and Z(G)$\mathrm{Z}(G)$ (standard zero forcing number) all satisfy the Graph Complement Conjecture (see Barioli et al. (2012) [3]). Graphs having extreme values of the positive semidefinite zero forcing number are characterized. The effect of various graph operations on positive semidefinite zero forcing number and connections with other graph parameters are studied.     

Solving generalized eigenvalue problems on the interfaces to build a robust two-level FETI method

FETI is a very popular method, which has proved to be extremely efficient on many large-scale industrial problems. One drawback is that it performs best when the decomposition of the global problem is closely related to the parameters in equations. This is somewhat confirmed by the fact that the theoretical analysis goes through only if some assumptions on the coefficients are satisfied. We propose here to build a coarse space for which the convergence rate of the two-level method is guaranteed regardless of any additional assumptions. We do this by identifying the problematic modes using generalized eigenvalue problems.     

Isomerizing olefin metathesis as a strategy to access defined distributions of unsaturated compounds from Fatty acids

The dimeric palladium(I) complex [Pd(μ-Br)(t)Bu(3)P](2) was found to possess unique activity for the catalytic double-bond migration within unsaturated compounds. This isomerization catalyst is fully compatible with state-of-the-art olefin metathesis catalysts. In the presence of bifunctional catalyst systems consisting of [Pd(μ-Br)(t)Bu(3)P](2) and NHC-indylidene ruthenium complexes, unsaturated compounds are continuously converted into equilibrium mixtures of double-bond isomers, which concurrently undergo catalytic olefin metathesis. Using such highly active catalyst systems, the isomerizing olefin metathesis becomes an efficient way to access defined distributions of unsaturated compounds from olefinic substrates. Computational models were designed to predict the outcome of such reactions. The synthetic utility of isomerizing metatheses is demonstrated by various new applications. Thus, the isomerizing self-metathesis of oleic and other fatty acids and esters provides olefins along with unsaturated mono- and dicarboxylates in distributions with adjustable widths. The cross-metathesis of two olefins with different chain lengths leads to regular distributions with a mean chain length that depends on the chain length of both starting materials and their ratio. The cross-metathesis of oleic acid with ethylene serves to access olefin blends with mean chain lengths below 18 carbons, while its analogous reaction with hex-3-enedioic acid gives unsaturated dicarboxylic acids with adjustable mean chain lengths as major products. Overall, the concept of isomerizing metatheses promises to open up new synthetic opportunities for the incorporation of oleochemicals as renewable feedstocks into the chemical value chain.     

Ozonolysis of bicyclic 1,2-dioxines: initial scope and mechanistic insights

The ozonolysis of bicyclic 1,2-dioxines was investigated using a variety of 1,4-disubstituted 1,2-dioxines along with a 1,3-dialkyl and steroidal example, with yields ranging from moderate to excellent. Two different pathways were observed upon reaction of the 1,4-disubstituted 1,2-dioxines with ozone; one pathway saw the "expected" results, that is, cleavage of the olefinic moiety with generation of 1,4-dicarbonyl 1,2-dioxines, while the other pathway revealed a previously unobserved rearrangement involving cleavage of the peroxide linkage along with loss of either CO or CO(2). Several unsymmetrical ozonolyses were also performed to further investigate the origins of this rearrangement, and initial mechanistic insights into the fragmentation pathways are discussed.     

Revisiting the polyoxometalate-based late-transition-metal-oxo complexes: the "oxo wall" stands

Terminal oxo complexes of the late transition metals Pt, Pd, and Au have been reported by us in Science and Journal of the American Chemical Society. Despite thoroughness in characterizing these complexes (multiple independent structural methods and up to 17 analytical methods in one case), we have continued to study these structures. Initial work on these systems was motivated by structural data from X-ray crystallography and neutron diffraction and (17)O and (31)P NMR signatures which all indicated differences from all previously published compounds. With significant new data, we now revisit these studies. New X-ray crystal structures of previously reported complexes K(14)[P(2)W(19)O(69)(OH(2))] and "K(10)Na(3)[Pd(IV)(O)(OH)WO(OH(2))(PW(9)O(34))(2)]" and a closer examination of these structures are provided. Also presented are the (17)O NMR spectrum of an (17)O-enriched sample of [PW(11)O(39)](7-) and a careful combined (31)P NMR-titration study of the previously reported "K(7)H(2)[Au(O)(OH(2))P(2)W(20)O(70)(OH(2))(2)]." These and considerable other data collectively indicate that previously assigned terminal Pt-oxo and Au-oxo complexes are in fact cocrystals of the all-tungsten structural analogues with noble metal cations, while the Pd-oxo complex is a disordered Pd(II)-substituted polyoxometalate. The neutron diffraction data have been re-analyzed, and new refinements are fully consistent with the all-tungsten formulations of the Pt-oxo and Au-oxo polyoxometalate species.     

Photolability of NO in designed metal nitrosyls with carboxamido-N donors: a theoretical attempt to unravel the mechanism

During the past few years, photoactive metal nitrosyls (NO complexes of metals) have drawn attention as potential drugs for delivery of nitric oxide (NO) to biological targets under the control of light. Major success in this area has been achieved with designed metal nitrosyls derived from ligands that contain carboxamide group(s). A number of iron, manganese and ruthenium {MNO}(6) nitrosyls of such kind exhibit excellent NO photolability under low-power visible and near-IR light. The results of theoretical studies on these NO-donors have provided insight into (a) the electronic transitions that lead to photorelease of NO and (b) the structural features of the ligands that dictate the sensitivity of the nitrosyls to light of specific wavelengths. In addition, the results have afforded clear understanding of the electronic configurations of the various nitrosyls. This article highlights these results in a coherent manner. Good matches between the predicted and observed spectral features and NO photolability strongly suggest that theoretical studies should be an integral part of the smart design of such NO-donors in the future research.     

Hydrogel Substrate Stiffness and Topography Interact to Induce Contact Guidance in Cardiac Fibroblasts

Previous studies demonstrated the importance of substrate stiffness and topography on the phenotype of many different cell types including fibroblasts. Yet the interaction of these two physical parameters remains insufficiently characterized, in particular for cardiac fibroblasts. Most studies focusing on contact guidance use rigid patterned substrates. It is not known how the ability of cardiac fibroblasts to follow grooves and ridges changes as the substrate stiffness is decreased to match the range of stiffness found in native heart tissues. This report demonstrates a significant interactive effect of substrate stiffness and topography on cardiac fibroblast elongation and orientation using polyacrylamide substrates of different stiffness and topography.