Observation of a bi-domain state and nucleation free switching in mesoscopic ring magnets

We present the results of a study of the magnetic properties of an array of 34-nm thick Co(100) epitaxial ring magnets, with inner and outer diameters of d(in) = 1.3 microm and d(out) = 1.6 microm, respectively. Magnetic measurements and micromagnetic simulations show that a two step switching process occurs at high fields, indicating the existence of two different stable states. In addition to the vortex state, which occurs at intermediate fields, we have identified a new bi-domain state, which we term the onion state, corresponding to opposite circulation of the magnetization in each half of the ring. The onion state is stable at remanence and undergoes a simple and well characterized nucleation free switching.     

Structural and morphological characterisation of hybrid Cu/Si(0 0 1) structures

The structural and morphological properties of epitaxial Cu/Si(0 0 1) type of structures have been investigated by a combination of electron, X-ray and scanning probe imaging techniques. Auger electron spectroscopy measurements indicate the presence of Si in the Cu layer for Cu thicknesses up to 10 nm. In addition, X-ray scattering results show that there is a mosaic spread in the Cu(0 0 1) crystal which decreases as the Cu thickness increases, from 8° at 15 nm to 4.5° at 100 nm. This behaviour is corroborated by reflection high energy electron diffraction patterns of the Cu surface measured during growth, which exhibit a twinning in the diffraction spots for the 15 and 30 nm Cu films. Atomic force and scanning electron microscopy imaging of Cu(4 nm)/Co(7,17 nm)/Cu(100 nm)/Si(0 0 1) structures allow one to visualise and characterise the sample surface in real space; from these measurements, an average roughness amplitude of ∼0.5 nm and a correlation length of ∼50 nm are obtained. Our results provide a better understanding of an important system which has been widely used as a template for the growth of epitaxial ultrathin magnetic films.     

An improved decomposition-based heuristic to design a water distribution network for an irrigation system

In this paper the authors address a pressurized water distribution network design problem for irrigation purposes. Two mixed binary nonlinear programming models are proposed for this NP-hard problem. Furthermore, a heuristic algorithm is presented for the problem, which considers a decomposition sequential scheme, based on linearization of the second model, coupled with constructive and local search procedures designed to achieve improved feasible solutions. To evaluate the robustness of the method we tested it on several instances generated from a real application. The best solutions obtained are finally compared with solutions provided by standard software. These computational experiments enable the authors to conclude that the decomposition sequential heuristic is a good approach to this difficult real problem.     

Globally convergent DC trust-region methods

In this paper, we investigate the use of DC (Difference of Convex functions) models and algorithms in the application of trust-region methods to the solution of a class of nonlinear optimization problems where the constrained set is closed and convex (and, from a practical point of view, where projecting onto the feasible region is computationally affordable). We consider DC local models for the quadratic model of the objective function used to compute the trust-region step, and apply a primal-dual subgradient method to the solution of the corresponding trust-region subproblems. One is able to prove that the resulting scheme is globally convergent to first-order stationary points. The theory requires the use of exact second-order derivatives but, in turn, the computation of the trust-region step asks only for one projection onto the feasible region (in comparison to the calculation of the generalized Cauchy point which may require more). The numerical efficiency and robustness of the proposed new scheme when applied to bound-constrained problems is measured by comparing its performance against some of the current state-of-the-art nonlinear programming solvers on a vast collection of test problems.     

Dynamic evanescent phonon coupling across the La(1-x)Sr(x)MnO3/SrTiO3 interface

The transport and magnetic properties of correlated La0.53Sr0.47MnO3 ultrathin films, grown epitaxially on SrTiO3, show a sharp cusp at the structural transition temperature of the substrate. Using a combination of experiment and first principles theory we show that the cusp is a result of evanescent cross-interface coupling between the charge carriers in the film and a soft phonon mode in the SrTiO3, mediated through linked oxygen octahedral motions. The amplitude of the mode diverges at the transition temperature, and phonons are launched into the first few atomic layers of the film, affecting its electronic state.     

Formation of pyranoanthocyanins in red wines: a new and diverse class of anthocyanin derivatives

Pyranoanthocyanins constitute one of the most important classes of anthocyanin-derived pigments occurring naturally in red wine. Nonetheless, correct assignment of their structures and pathways of formation in red wine has been relatively recent—less than two decades. Study of these newly discovered pigments is progressively unfolding the chemical pathways that drive the evolution of red wine colour during ageing. The objective of this paper is to review current knowledge regarding the pathway of formation in red wine of a great variety of pyranoanthocyanin structures, namely carboxypyranoanthocyanins, methylpyranoanthocyanins, pyranoanthocyanin-flavanols, pyranoanthocyanin-phenols, portisins, oxovitisins, and pyranoanthocyanin dimers. The chromatic features of some of the compounds, for example their colour expression and acid–base equilibria in aqueous media, are also discussed.     

Catalytic asymmetric diastereodivergent deracemization

Your wish is my command: Deracemization is a powerful strategy wherein a racemate is converted into a 100?% yield of a single enantiopure product. A new concept in catalytic deracemization is presented, in which a racemate with n?stereogenic elements can be selectively converted into each one of 2(m) (m = number of chiral centers of the product) different enantiopure products, by simple tuning of the reaction conditions.     

Predicting hydration Gibbs energies of alkyl-aromatics using molecular simulation: a comparison of current force fields and the development of a new parameter set for accurate solvation data

The Gibbs energy of hydration is an important quantity to understand the molecular behavior in aqueous systems at constant temperature and pressure. In this work we review the performance of some popular force fields, namely TraPPE, OPLS-AA and Gromos, in reproducing the experimental Gibbs energies of hydration of several alkyl-aromatic compounds--benzene, mono-, di- and tri-substituted alkylbenzenes--using molecular simulation techniques. In the second part of the paper, we report a new model that is able to improve such hydration energy predictions, based on Lennard Jones parameters from the recent TraPPE-EH force field and atomic partial charges obtained from natural population analysis of density functional theory calculations. We apply a scaling factor determined by fitting the experimental hydration energy of only two solutes, and then present a simple rule to generate atomic partial charges for different substituted alkyl-aromatics. This rule has the added advantages of eliminating the unnecessary assumption of fixed charge on every substituted carbon atom and providing a simple guideline for extrapolating the charge assignment to any multi-substituted alkyl-aromatic molecule. The point charges derived here yield excellent predictions of experimental Gibbs energies of hydration, with an overall absolute average deviation of less than 0.6 kJ mol(-1). This new parameter set can also give good predictive performance for other thermodynamic properties and liquid structural information.     

A different way to verify the violation of the WWŻB inequality

The solution to Bell theorem for N-qubits was widely studied in [M. ?ukowski, ?. Brukner, Phys. Rev. Lett. 88, 210401 (2002)]. Here we present a different way to obtain the solution of that theorem for the dichotomic experiment. In order to obtain a solution for the Werner-Wolf-?ukowski-Brukner WW?B inequality a new correlation function is proposed. This new correlation function expresses directly the constraints imposed by local theories. We use the general Greenberger-Horne-Zeilinger (GHZ) state, whereof, as it is well known, emerges a family of entangled states that do not violate the WW?B inequality [M. ?ukowski, ?. Brukner, W. Laskowski, M. Wie?niak, Phys. Rev. Lett. 88, 210402 (2002)], i.e. it can be described by a local realistic theory, to illustrate our results.     

Total Synthesis of Enantiopure Pyrrhoxanthin: Alternative Methods for the Stereoselective Preparation of 4‐Alkylidenebutenolides

A new stereocontrolled total synthesis of the configurationally labile C₃₇‐norcarotenoid pyrrhoxanthin in enantiopure form has been completed. A highly stereoselective Horner–Wadsworth–Emmons (HWE) condensation of a C₁₇‐allylphosphonate and a C₂₀‐aldehyde was used as the last conjunctive step. Both a Sonogashira reaction to form the C₁₇‐phosphonate and the final HWE condensation proved to be compatible with the sensitive C7–C10 enyne E configuration. Regioselective (5‐exo‐dig) silver‐promoted lactonization reactions of three alternative pent‐2‐en‐4‐ynoic acid precursors with increased complexity, including a fully functionalized C₂₀‐fragment, were explored for the preparation of the γ‐alkylidenebutenolide fragment. This survey extends the existing methodologies for the preparation of oxygen‐containing carotenoids (xanthophylls) and streamlines the synthesis of additional members of the C₃₇‐norcarotenoid butenolide family of natural products.