Almost Complex Structures Which Are Compatible with Kähler or Symplectic Structures

In this note we prove that half of all homotopy classes of almost complex structures on M is not compatible with any symplectic structure for a certain class of oriented compact 4-manifolds M. In particular, half of all homotopy classes of almost complex structures on an oriented 4-manifold is not compatible to any Kähler structure.     

Spatiotemporal stochastic resonance and its consequences in neural model systems

The realization of spatiotemporal stochastic resonance is studied in a two-dimensional FitzHugh-Nagumo system, and in a one-dimensional system of integrate-and-fire neurons. We show that spatiotemporal stochastic resonance occurs in these neural model systems, independent of the method of modeling. Moreover, the ways of realization are analogous in the two model systems. The biological implications and open questions are discussed. (c) 2001 American Institute of Physics.     

Modified quadrature formulas for functions with nearby poles

This paper is concerned with the numerical integration of functions with poles near the interval of integration. A method is given for modifying known quadrature rules, to obtain rules which are exact for certain classes of rational functions.     

On automorphisms of vector bundles

A finite group G is isomorphic to a group of automorphisms of a real indecomposable vector bundle ψ over a paracompact space B if and only if G is isomorphic to a subgroup of the multiplicative group of the division algebra of real quaternions.     

Characterizing the influence of reinforcing resin on the structure and the mechanical response of filled isoprene rubber

In the present study, a specific type of reinforcing resin behavior is investigated using various mechanical approaches as well as microscopic techniques such as transmission electron microscopy and atomic force microscopy. Based on these observations, it could be concluded that the reinforcing resin introduces a synergistic effect with carbon black in order to strengthen the system. This is implied since the percolation threshold is significantly reduced and the morphology of the filler aggregates changes toward higher compactness, i.e., an increase of volume-to-size ratio with the addition of resin.     

Towards the Design of Optically Active Thiophene S-Oxides using Quantum Chemistry

The importance of axially chiral biaryls has risen steeply in the recent decades. This structural motif proved to be successful in catalytic asymmetric synthesis and the configuration of the biaryl axis is decisive for the biological activity. A new approach for the atroposelective synthesis of biaryls would be through a cycloaddition between an enantiopure phenyl-substituted thiophene S-oxide and an alkyne. Importantly, the chiral center of the thiophene S-oxide needs to be stable enough to avoid pyramidal inversion during the cycloaddition. Considering that the racemization of thiophene monoxides has been scarcely investigated so far, we perform a thorough quantum chemical study on the inversion barriers of a large number of chiral thiophene S-oxide derivatives. Our main goal is to identify substitution patterns leading to stable atropisomers at room temperature. Appealingly, the role of stereoelectronic effects and the position of the substituents as well as the importance of aromaticity on the pyramidal inversion barrier are elucidated for the first time.     

New Studies on Humphry Davy: Introduction

This special issue of Ambix brings together eight new studies on Humphry Davy together with an appreciation of the life and work of David Knight, much of whose scholarship was devoted to understanding Davy. Taken together they provide a much richer and more nuanced account of aspects of Davy’s life, showing how he and his work fitted into the very complex and difficult social, cultural and political contexts of the opening decades of the nineteenth century. Taking as our starting point Thomas Carlyle’s 1829 critique of modern science, in this introduction we weld together the themes that emerge from these papers, many of which ground their results in the project to publish Davy’s Letters. This project has provided evidence that helps us critique the disciplinary boundaries that led to Davy becoming seen mostly as a chemist, while his friend Samuel Taylor Coleridge has generally been categorised as a poet. Such boundaries are now breaking down fruitfully as these essays all illustrate in their different ways. A consequence of the new understandings being produced, is that we need to consider anew what constitutes chemistry and chemists, how reputations and commemorations are constructed, the role of audiences (especially women) in developing knowledge and the use of language and literature, which, among other things, are key elements linking chemistry with other parts of society and culture. Davy provides an excellent location by which to address the historical issues involved, giving us an opportunity to balance carefully these and other components (such as human agency) in understanding how knowledge is constructed.     

Synthesis,Hirshfeld surface analysis,luminescence and thermal properties of three first-row transition metal complexes containing 4′-hydroxy-2,2′:6′,2″-terpyridine: Application for preparation of nano metal oxides

A series of new mono- and bis-terpyridine complexes [Mn(tpyOH)Cl₂] ( 1 ), [Ni(tpyOH)₂](PF₆)₂ ( 2 ) and [Zn(tpyO)(η¹-OCOCH₃)(H₂O)]⋅3H₂O ( 4 ) containing 4′-hydroxy-2,2′:6′,2″-terpyridine (tpyOH) were synthesized and structurally characterized using elemental analysis, infrared spectroscopy and single-crystal X-ray diffraction. The reaction of MnCl₂ with tpyOH in a mixture of methanol and CH₂Cl₂ resulted in the formation of 1 . The X-ray crystal structure of 1 reveals that Mn(II) is penta-coordinated by three nitrogen atoms from tpyOH and two Cl⁻ in a slightly distorted trigonal bipyramidal geometry. Complex 2 was also prepared by the reaction of nickel(II) chloride with tpyOH in a methanolic medium in the presence of NH₄PF₆. Notably, the complex [Ni(tpyOH)(tpyO)]PF₆ ( 3 ), obtained during the crystallization of 2 from dichloromethane, was characterized using X-ray crystallography which shows that six nitrogen atoms from terpyridine ligands occupy the coordination sites around the Ni(II) centre in a distorted octahedral geometry with four longer bonds and two shorter Ni N bonds. The reaction of zinc(II) acetate with tpyOH in a mixture of methanol and CH₂Cl₂ led to the formation of 4 . The crystal structure of 4 reveals the formation of penta-coordinated Zn(II) complex containing three nitrogen atoms from tpyO, a monodentate acetate ligand and one coordinated water molecule. Hirshfeld surface analyses and two-dimensional fingerprint plots show that the main interactions are O…H/H…O contacts in 1 , 3 and 4 . The thermal decomposition reactions of 1 , 2 and 4 were studied using thermogravimetric analysis in detail due to their different structures. The solution luminescence features of 1 , 2 and 4 include high-energy intense π → π* intraligand and low-energy metal-to-ligand charge transfer transitions at room temperature. The calcination of the coordination complexes led to the formation of corresponding nano metal oxides. The products were structurally characterized using infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The average particle size using Scherrer's equation was calculated to be below 50 nm.     

Dimension reduction for semidefinite programs via Jordan algebras

Mathematical Programming - We propose a new method for simplifying semidefinite programs (SDP) inspired by symmetry reduction. Specifically, we show if an orthogonal projection map satisfies...