Selectively protected galactose derivatives for the synthesis of branched oligosaccharides

Synthesis and characterization of several new anomerically pure galactose derivatives, based on simple and effective protective group manipulations of benzyl β-d-galactopyranoside, are reported. The monosaccharides described contain selectively protected/deprotected hydroxyl functionalities at their 1,2,3,4- and 6-positions rendering them useful as building blocks for construction of branched oligosaccharides.     

Click chemistry in materials synthesis. III. Metal‐adhesive polymers from Cu(I)‐catalyzed azide–alkyne cycloaddition

1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007     

Physical processes underlying the development of shear turbulence

A physical model of the development of turbulence in free shear flows is proposed. The model is based on the results of numerical simulations of turbulent flow development. The main ideas of the proposed theory of turbulence are stated as follows: the onset of turbulence begins with the formation of large vortices; spectral energy transfer involves both direct and inverse cascades; and the inertial range of the energy spectrum develops as a result of concurrent direct and inverse cascades. The dominant physical factors that determine the spectrum include Joukowski forces.     

Computing the sound power in non-uniform flow

An expression for the sound power in an annular duct with swirling mean flow is derived in the high-frequency limit relevant to fan aeroacoustics. The sound power is expressed in terms of the duct normal modes which are computed for several mean flows. It is shown that the mean flow non-uniformity modifies both the pressure-dominated modes and the expression for the sound power. The pressure-dominated modes are not orthogonal and thus one must account for interference between the different radial modes. The interference effects are small for the case of a potential mean flow. For a vortical mean flow interference terms may become significant.     

First-principles calculations of the hyperfine fields on ligands in fluorides

In solid-state physics, a crystal lattice is frequently approximated by an array of interacting ions. In this case, the wave functions of individual ions are assumed to be a fairly good zeroth approximation in calculating the matrix elements of the interaction Hamiltonian of electrons and nuclei of the lattice from first principles. Use of the second-quantization method is proposed for such calculations in the basis of these functions. As an example, the electron transition amplitude from a ligand to the central ion is estimated. The results agree well with the experimental data.