Dimerization in the magnetostrictive one-dimensional XY model

We discuss the one-dimensional first-neighbor $\text{1}\text{2}$-spin magnetostrictive XY model (where the crystalline degrees of freedom are assumed to be three- dimensional), and exhibit that, for all temperatures below T_c, no other contributions to the structural order appear than the pure dimerization one. The influences of temperature and elastic constant on the order parameter and sound velocity are analyzed as well.     

Numerical calculation of the dielectric and electrokinetic properties of vesicle suspensions

The dielectric and electrokinetic properties of aqueous suspensions of vesicles (unilamellar liposomes) are numerically calculated in the 1 Hz to 1 GHz frequency range using a network simulation method. The model consists of a conducting internal medium surrounded by an insulating membrane with fixed surface charges on both sides. Without an applied field, the internal medium is in electric equilibrium with the external one, so that it also bears a net volume charge. Therefore, in the presence of an applied ac field, there is fluid flow both in the internal and in the external media. The obtained results are qualitatively different from those corresponding to suspensions of charged homogeneous particles, mainly due to the existence of an additional length scale (the membrane thickness) and the corresponding dispersion mechanism, charging of the membrane. Because of this dispersion, the shapes of the spectra change with the size of the particles (at constant zeta potential and particle radius to Debye length ratio) instead of merely shifting along the frequency axis. A comparison between the numerical results and those obtained using approximate analytical expressions shows deviations that are, in general, sufficiently large enough to show the necessity to use numerical results in order to interpret broad frequency range dielectric and electrokinetic measurements of vesicle suspensions.     

Synthesis of 1-methyl-3-oxo-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid methyl ester

A simple and efficient method for the preparation of 1-methyl-3-oxo-7- oxabicyclo[2.2.1]hept-5-en-2-carboxylic acid methyl ester (1) is described. The first step is a highly regioselective Diels-Alder reaction between 2-methylfuran and methyl-3-bromo- propiolate. A remarkably difficult ketal hydrolysis reaction was effected by treatment with HCl, a simple reagent that was shown to be more efficient, in this case, than commonly used more elaborate methods.     

Simple and multiple scattering in disordered one-dimensional media: Renormalisation group approach

The exact characteristic penetration length associated with both simple and multiple incoherent elastic scattering in semi-infinite one-dimensional disordered media is established as a function ofp (concentration of scattering centers) andf ₀ (transmission coefficient of a single center). Then we exhibit how these phenomena can be seen as critical ones, and the corresponding are reobtained within convenient real space renormalisation group frameworks. Finally we discuss a generalized model where the single center transmission coefficientf can randomly take two different valuesf ₁ andf ₂.     

Phase diagram of the Hubbard model with arbitrary band filling

The finite temperature phase diagram of the Hubbard model ind=2 andd=3 is calculated for arbitrary values of the parameterU/t and chemical potential using a quantum real space renormalization group. Evidence for a ferromagnetic phase at low temperatures is presented.     

Specific heat of the anisotropic rigid rotator

The exact (numerical) thermal evolution of the specific heatC of the single anisotropic (not necessarily equal inertial momentaI _x I _y I _xy andI ₂) quantum rigid rotator is calculated. For values ofI _xy /I _z low enough,C presents an unexpectedly high maximum; for sufficiently high values ofI _xy /I _z a second peak emerges. Also a quite rich T0 asymptotic behavior is exhibited.     

High stereoselectivity on low temperature Diels-Alder reactions

We have found that some of the usually poor dienophiles (2-cycloenones) can undergo Diels-Alder reaction at -78 degrees C with unusually high stereoselectivity in the presence of niobium pentachloride as a Lewis acid catalyst. A remarkable difference in reaction rates for unsubstituted and alpha- or beta-methyl substituted 2-cycloenones was also observed.     

A short and efficient synthesis of crocetin-dimethylester and crocetindial

In this paper we describe an efficient six-step synthesis of crocetin-dimethylester that could be further reduced to a "four-step" synthesis through the use of in situ procedures. The simplicity of the whole process, the ready availability of starting materials, and the high overall yield render this strategy a very attractive synthesis of this very important compound, which is the key intermediate for the synthesis of several carotenoids and other polyene natural products.     

Preparation and Characterization of Cu(II) Phthalocyanine Tetrasulfonate Intercalated and Supported on Layered Double Hydroxides

The aim of the present work was to synthesize and characterize layered doublehydroxides (LDHs), in the magnesium/aluminum form, intercalated with copper(II)phthalocyanine tetrasulfonate (CuPcTs). The metal complex was immobilized intothe LDH gallery region through the reconstitution method and this material wascharacterized by X-ray diffraction (XRD), surface area and porosity measurements,elementary analysis, thermogravimetry (TGA), vibrational (IR) and electronic(UV-visible) spectroscopies, and electronic paramagnetic resonance (EPR). Thecatalytic performance of CuPcTs intercalated and supported on the LDH wasevaluated by carrying out the hydrogen peroxide dismutation. The CuPcTs wassuccessfully intercalated into the LDH layers according to XRD data (the basalspacing of the carbonate precursors increases by approximately 15Å inthe intercalated samples). The surface area and porosity analysis suggested thatthe CuPcTs intercalated materials are not microporous solids. Samples containingthe metal complex confined between the LDH layers have an appreciable thermalstability: decomposition is not observed at least up to 400 °C. TGA experiments also show that the weight-loss curves of the CuPcTs supported samples superimpose those recorded for the CuPcTs complex and the LDH-carbonate while the curves for theintercalated materials are unique. CuPcTs intercalated or supported on LDHs is notactive in the hydrogen peroxide dismutation although the free form shows activity at pH above 8.