Organocatalytic regioselective Michael additions of cyclic enones via asymmetric phase transfer catalysis

Cyclohexanone and cycloheptanone can be enantioselectively functionalized in the 3-position with up to 92% ee and 87% ee, respectively, by the base-promoted dimerization of the corresponding enones using 3,4,5-tribenzyloxybenzyl cinchoninium bromide, as a new effective catalyst.     

Optical properties of single semiconductor nanocrystals

We present an overview of the current progress in the understanding of the (steady state) optical properties of individual II-VI semiconductor nanocrystals. We begin with a presentation of the conceptual development of the theory required to model the electronic structure of these systems. This is followed by an overview of the current experimental results obtained from the spectroscopy of individual semiconductor nanocrystals, and in particular, we focus on the study of photoluminescence intermittency (blinking) and spectral diffusion. Where possible, we link the experimental observations to the predictions of current theories. We conclude that the surface of small semiconductor crystals plays an important role in determining their optical properties.     

Stereoselective synthesis of the cytotoxic macrolide FD-891

[reaction: see text] A total synthesis of the naturally occurring, cytotoxic macrolide FD-891 is described. Three fragments were first stereoselectively constructed using mainly asymmetric aldol and allylation reactions. The complete framework was then assembled using two Julia-Kocienski olefinations to connect the three fragments and a Yamaguchi reaction to close the macrolactone ring.     

A luminescent probe containing a tuftsin targeting vector coupled to a terbium complex

Orthogonal protection strategies have been used to prepare a series of luminescent and MRI active lanthanide complexes containing a tuftsin targeting vector that are internalised by macrophage cells.     

Control of hysteretic instability in rotating machinery by elastic suspension systems subject to dry and viscous friction

Most of the undesired whirling motions of rotating machines can be efficiently reduced by supporting journal boxes elastically and controlling their movement by viscous dampers or by dry friction surfaces normal to the shaft axis, which rub against the frame. In the case of dry dampers, resonance ranges of the floating support configuration can be easily cut off by planning a motionless adhesive state of the friction surfaces. On the contrary, the dry friction contact must change automatically into sliding conditions when the fixed support resonances are to be feared. Moreover, the whirl amplitude can be restrained throughout the speed range by a proper choice of the suspension-to-shaft stiffness ratio and of the support-to-rotor mass ratio.This theoretical research deals firstly with the natural precession speeds and looks for Campbell plots in dependence on the shaft angular speed, for several rotor-suspension systems. Then, the steady response to unbalance is investigated, in terms of rotor and support orbits and of conical path of the rotor axis. In this search, the ranges of adhesive or sliding contact are identified in particular for system with dry friction damping. At last, the destabilizing influence of the shaft hysteresis in the supercritical regime is focalized and the counterbalancing effect of the other dissipative sources is verified. In the nonlinear case of dry friction dampers, the control of linear stability is fulfilled by a perturbation procedure, checking the magnitude of Floquet characteristic multipliers on the complex plane. Moreover, the nonlinear stability far from steady motion is tested by the direct numerical solution of the full motion equations. The comparison configuration of suspension systems with viscous dampers and no dry friction is examined through an analytical first approximation approach and closed-form results for stability thresholds are derived in particular for the symmetric case.     

Stable hypersurfaces via the first eigenvalue of the anisotropic Laplacian operator

In this paper we provide a characterization for stable hypersurfaces with constant anisotropic mean curvature immersed in the Euclidean space \(\mathbb {R}^{n+1}\) through the analysis of the first eigenvalue of the anisotropic Laplacian operator.     

A note on total degree polynomial optimization by Chebyshev grids

Using the approximation theory notions of polynomial mesh and Dubiner distance in a compact set, we derive error estimates for total degree polynomial optimization on Chebyshev grids of the hypercube.     

Disentangling price,risk and model risk: V&R measures

We propose a method to assess the intrinsic risk carried by a financial position X when the agent faces uncertainty about the pricing rule assigning its present value. Our approach is inspired by a new interpretation of the quasiconvex duality in a Knightian setting, where a family of probability measures replaces the single reference probability and is then applied to value financial positions. Diametrically, our construction of Value and Risk measures is based on the selection of a basket of claims to test the reliability of models. We compare a random payoff X with a given class of derivatives written on X, and use these derivatives to “test” the pricing measures. We further introduce and study a general class of Value and Risk measures \( R(p,X,\mathbb {P})\) that describes the additional capital that is required to make X acceptable under a probability \(\mathbb {P}\) and given the initial price p paid to acquire X.     

On the Lebesgue constant for the Xu interpolation formula

In the paper [Y. Xu, Lagrange interpolation on Chebyshev points of two variables, J. Approx. Theory 87 (1996) 220–238], the author introduced a set of Chebyshev-like points for polynomial interpolation (by a certain subspace of polynomials) in the square [-1,1]², and derived a compact form of the corresponding Lagrange interpolation formula. In [L. Bos, M. Caliari, S. De Marchi, M. Vianello, A numerical study of the Xu polynomial interpolation formula in two variables, Computing 76(3–4) (2005) 311–324], we gave an efficient implementation of the Xu interpolation formula and we studied numerically its Lebesgue constant, giving evidence that it grows like , n being the degree. The aim of the present paper is to provide an analytic proof to show that the Lebesgue constant does have this order of growth.