Semi-Absolute Deviation Rule for Mutual Funds Portfolio Selection

Investors consider mutual funds as an interesting investment opportunity. This is the result of the impressive growth shown by these financial products in recent times. In this paper we propose a mixed integer linear programming model dealing with the portfolio selection problem on mutual funds in a single period investment strategy. We propose some heuristics and compare their performance. According to the results obtained on real instances, heuristics have proved to be effective and efficient.     

A re-examination of the methylenation reaction

A re-examination of the methylenation reaction of 1-hydroxy-2-mercapto-, 1,2-dihydroxy- and 1,2-dimercapto-substituted benzenes by bromochloromethane with cesium carbonate shows that these substrates give mixtures of five- and ten-membered benzocondensed heterocyclic compounds and in some cases even dibenzodioxines.     

Permeation,diffusion, and sorption of dimethyl ether in fluoroelastomers

The permeation, diffusion, and sorption of dimethyl ether into a series of commercial fluoroelastomers were characterized at various pressures and temperatures. The polymers under study were based on tetrafluoroethylene and contained various amounts of other perfluorinated monomers: perfluoromethylvinylether, hexafluoropropylene, and a partially fluorinated monomer, vinylidene fluoride (VDF). These polymers were also filled with inorganic particles and cured with different techniques. The permeation rate of dimethyl ether in the elastomers examined, as well as the solubility value, increased as the content of the nonperfluorinated monomer (VDF) increased, and this was consistent with the solubility parameter theory. The diffusion coefficients, at a fixed concentration, had rather similar values for most of the elastomers examined. Both the permeability and diffusivity increased with temperature, and the corresponding activation energies were obtained for two selected polymers. The solubility of dimethyl ether, at a fixed temperature and activity, showed a linear dependence versus the weight fraction of the partially fluorinated monomer (VDF) in the polymeric matrix. The effect of the filler on the sorption and transport properties was also considered: the addition of the filler lowered the permeability and diffusivity, whereas the solubility was generally increased with respect to the crosslinked rubber. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1987–2006, 2004     

Host–Guest Chemistry of Aromatic‐Amide‐Linked Bis‐ and Tris‐Calix[4]pyrroles with Bis‐Carboxylates and Citrate Anion

A small library of polytopic receptors has been synthesized from meso‐p‐ and meso‐m‐aminophenylcalix[4]pyrroles and p‐ or m‐phthaloyl or trimesic chloride. Selected bis‐carboxylates and the citrate anion, which either exhibit altered distribution profiles in cancerous tissues in comparison with healthy tissues or are metabolites of carcinogenic substances (for example, trans,trans‐muconic acid from benzene exposure in humans) were tested as ligands. Varied affinities and binding modes were observed as a function of the number of calix[4]pyrroles and the topology of amide units present in each of the polytopic receptors. The structures of the 1:1 complexes derived by molecular modeling are in excellent agreement with the results of ¹H NMR complexation studies.     

Multiple headspace-solid-phase microextraction: An application to quantification of mushroom volatiles

Multiple headspace-solid phase microextraction (MHS-SPME) followed by gas chromatography/mass spectrometry (GC–MS) and flame ionization detection (GC–FID) was applied to the identification and quantification of volatiles released by the mushroom Agaricus bisporus, also known as champignon. MHS-SPME allows to perform quantitative analysis of volatiles from solid matrices, free of matrix interferences. Samples analyzed were fresh mushrooms (chopped and homogenized) and mushroom-containing food dressings. 1-Octen-3-ol, 3-octanol, 3-octanone, 1-octen-3-one and benzaldehyde were common constituents of the samples analyzed. Method performance has been tested through the evaluation of limit of detection (LoD, range 0.033–0.078 ng), limit of quantification (LoQ, range 0.111–0.259 ng) and analyte recovery (92.3–108.5%). The results obtained showed quantitative differences among the samples, which can be attributed to critical factors, such as the degree of cell damage upon sample preparation, that are here discussed. Considerations on the mushrooms biochemistry and on the basic principles of MHS analysis are also presented.     

Structural Characterization of a Zinc High‐affinity Binding Site in Rhodopsin†

For the first time to our knowledge, X‐ray absorption spectroscopy (XAS) has been used to investigate the environment of putative Zn²⁺ binding sites in rhodopsin. We studied native purified nondeionized rhodopsin without any further addition of Zn²⁺, as well as with 1.5 mol of Zn²⁺—as zinc chloride—per mole of protein. Three different binding sites in rhodopsin were considered based on computational chemistry studies, and a quantitative analysis of the XAS signal was performed by fitting the experimental data to their simulated XAS spectra. Our results demonstrate that Zn²⁺ is intrinsically bound to rhodopsin and are compatible with the existence of an octahedral coordination involving six oxygen atoms in the first shell (average Zn‐O distance of 2.08 Å), and with a second coordination shell containing one or two phosphorus or sulfur atoms at an average distance of 2.81 Å.     

Pulse EPR Methods for Studying Chemical and Biological Samples Containing Transition Metals

This review discusses the application of pulse EPR to the characterization of disordered systems, with an emphasis on samples containing transition metals. Electron nuclear double‐resonance (ENDOR), electron‐spin‐echo envelope‐modulation (ESEEM), and double electron–electron resonance (DEER) methodologies are outlined. The theory of field modulation is outlined, and its application is illustrated with DEER experiments. The simulation of powder spectra in EPR is discussed, and strategies for optimization are given. The implementation of this armory of techniques is demonstrated on a rich variety of chemical systems: several porphyrin derivatives that are found in proteins and used as model systems, otherwise highly reactive aminyl radicals stabilized with electron‐rich transition metals, and nitroxide–copper–nitroxide clusters. These examples show that multi‐frequency continuous‐wave (CW) and pulse EPR provides detailed information about disordered systems.     

Gap orders of rational functions on plane curves with few singular points

We prove that certain integers n cannot occur as degrees of linear series without base points on the normalization of a plane curve whose only singularities are a “small” number of nodes and ordinary cusps. As a consequence we compute the gonality of such a curve. Work done with financial support of M.U.R.S.T. while the authors were members of C.N.R.