Cross section for the H+H2O abstraction reaction: experiment and theory

The absolute value of the cross section for the abstraction reaction between fast H atoms and H2O has been determined experimentally at a mean collision energy of 2.46 eV. The OH population distribution at the same mean energy has also been determined. The new measurements are compared with state-of-the-art quantum mechanical and quasiclassical scattering calculations on the most recently developed potential energy surface.     

Background noise in piezoresistive,electret condenser,and ceramic microphones

Background noise studies have been extended from air condenser microphones to piezoresistive, electret condenser, and ceramic microphones. Theoretical models of the respective noise sources within each microphone are developed and are used to derive analytical expressions for the noise power spectral density for each type. Several additional noise sources for the piezoresistive and electret microphones, beyond what had previously been considered, were applied to the models and were found to contribute significantly to the total noise power spectral density. Experimental background noise measurements were taken using an upgraded acoustic isolation vessel and data acquisition system, and the results were compared to the theoretically obtained expressions. The models were found to yield power spectral densities consistent with the experimental results. The measurements reveal that the 1/f noise coefficient is strongly correlated with the diaphragm damping resistance, irrespective of the detection technology, i.e., air condenser, piezoresistive, etc. This conclusion has profound implications upon the expected 1/f noise component of micromachined (MEMS) microphones.     

Addition of dipropylamine to multiacrylate and its model compound catalyzed by lithium dipropylamide

The nucleophilic addition reaction of dipropylamine to vinyl groups of multiacrylate - poly(2-acryloyloxyethyl methacrylate) and to 2-butyrylethyl acrylate as model compound has been investigated. Based on the results obtained, it has been shown that the addition reaction rate of dipropylamine to multiacrylate and 2-butyrylethyl acrylate is proportional to [CH₂=CH-] and to [(C₃H₇)₂NLi] with the ratio [(C₃H₇)₂NH]_o/[(C₃H₇)₂NLi]_o = 20. Second-order addition reaction rate constants and activation energies for the systems under investigation have been determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of dihydrofurocoumarins via palladium-catalyzed annulation of 1,3-dienes by o-iodoacetoxycoumarins

[reaction: see text] A variety of biologically interesting dihydrofurocoumarins have been synthesized in high yields by the palladium-catalyzed annulation of 1,3-dienes by o-iodoacetoxycoumarins. This reaction is very general and regioselective, and a wide variety of terminal, cyclic, and internal 1,3-dienes can be utilized.     

Crown Inclusion Compounds with 3,4-Diamino-1,2,5-Oxadiazole. X-Ray Structures of Its 1:1 Inclusion Complexes with 15-Crown-5 and Benzo-15-crown-5

The X-ray crystal structures of two closely related molecular complexes of 15-crown-5 and benzo-15-crown-5 with 3,4-diamino-1,2,5-oxadiazole are reported (I and II). Both complexes are of 1:1 stoichiometry with the host–guest alternation in the infinitechains formed due to the unsymmetrical H-bonding patterns between the components. Crystals of I are monoclinic, P2_1/c, a = 7.856(3), b = 12.994(1), c = 16.033(1) , = 94.79(2)°, Z = 4, final R-factor is 0.0488. Crystals of II are orthorhombic, P2₁2₁2₁, a = 8.260(4), b = 15.692(5),c = 13.955(7) , Z = 4, final R-factor is 0.0522.     

Rate of Convergence in Homogenization of Parabolic PDEs

We consider the solutions to /tu ⁽ⁿ⁾=a ⁽ⁿ⁾(x)u ⁽ⁿ⁾ where {a ⁽ⁿ⁾(x)} _n=1,2,... are random fields satisfying a well-mixing condition (which is different to the usual strong mixing condition). In this paper we estimate the rate of convergence of u ⁽ⁿ⁾ to the solution of a heat equation. Since our equation is of simple form, we get quite strong result which covers the previous homogenization results obtained on this equation.     

On Borel Sets in Function Spaces with the Weak Topology

It is proved that the duality map ,:(, weak)x(()*, weak*)R isnot Borel. More generally, the evaluation e:(C)(K),x KR, e(f,x) = f(x), is not Borel for any function space C(K) on a compactF-space. It is also shown that a non-coincidence of norm-Boreland weak-Borel sets in a function space does not imply thatthe duality map is non-Borel.     

Dynamic Global Constraints in Backtracking Based Environments

Global constraints provide strong filtering algorithms to reduce the search space when solving large combinatorial problems. In this paper we propose to make the global constraints dynamic, i.e., to allow extending the set of constrained variables during search. We describe a generic dynamisation technique for an arbitrary monotonic global constraint and we compare it with the semantic-based dynamisation for the alldifferent constraint. At the end we sketch a dynamisation technique for non-monotonic global constraints. A comparison with existing methods to model dynamic problems is given as well.     

On non-measurability of in its second dual

We show that with the weak topology is not an intersection of Borel sets in its Cech-Stone extension (and hence in any compactification). Assuming (CH), this implies that has no continuous injection onto a Borel set in a compact space, or onto a Lindelöf space. Under (CH), this answers a question of Arhangel'ski.

     

Minimal number of singular fibers in a Lefschetz fibration

There exists a (relatively minimal) genus Lefschetz fibration with only one singular fiber over a closed (Riemann) surface of genus iff and . The singular fiber can be chosen to be reducible or irreducible. Other results are that every Dehn twist on a closed surface of genus at least three is a product of two commutators and no Dehn twist on any closed surface is equal to a single commutator.