Synthesis and antifungal activity against strains of candida albicans of 6‐fluoro‐4(5 or 7)‐chloro‐2‐(difluorobenzoyl)aminobenzothiazoles

A series of 6‐fluoro‐4‐(5 or 7)‐chloro‐2‐(difluorobenzoyl)aminobenzothiazoles 3a‐r were prepared to investigate their potential biological activity. In this work, the results of their in vitro antifungal activity against some strains of Candida albicans are reported. It was found that some derivatives displayed antifungal activity higher than that for 3k [1a] compound already described in literature.     

New ramsdellites LiTi2−yVyO4 (0≤y≤1): Synthesis, structure, magnetic properties and electrochemical performances as electrode materials for lithium batteries

The new ramsdellite series LiTi_2−yV_yO₄ (0≤y≤1) has been prepared by conventional solid state chemistry techniques and was characterized by X-ray powder diffraction and electron diffraction. To our knowledge, this is the first report on ramsdellites containing vanadium. The magnetic behaviour of these ramsdellites is strongly influenced by its vanadium content. In this sense, LiTi₂O₄ (y=0) exhibits metallic-like temperature independent paramagnetism, but d electrons tend to localize with increasing V content. LiTiVO₄, though also paramagnetic, follows then the Curie-Weiss law. The crossover from delocalized to localized electrons is observed between compositions y=0.6 and 0.8. For y≥0.8 the magnetic results evidence an isovalent substitution mechanism of trivalent Ti by V. The electrochemical lithium intercalation and deintercalation chemistry of LiTi_2−yV_yO₄ is grouped into two different operating voltage regions. Reversible lithium deintercalation of vanadium-substituted ramsdellite titanates LiTi_2−yV_yO₄ in the high voltage range 2-3 V vs. Li occurs in two main steps, one at about 2 V and the other at about 3 V. The 3 V process capacity increases with the vanadium content, while the 2 V capacity decreases at the same time. The vanadium to titanium substitution rate in LiTi₂O₄ was found to be beneficial to the specific energy in as much as a 50% increase (1 V) of the working voltage is observed. On the other hand, reversible lithium intercalation in vanadium-substituted ramsdellite titanates LiTi_2−yV_yO₄ in the low voltage range 1-2 V vs. Li occurs in one main single step, in which the capacity is not affected by the vanadium content, although vanadium-doping produces an improved capacity retention with an excellent cycling behaviour observed for y≤0.6.     

Connections to fixed points and Sil’nikov saddle-focus homoclinic orbits in singularly perturbed systems

We consider a singularly perturbed system depending on two parameters with two (possibly the same) normally hyperbolic center manifolds. We assume that the unperturbed system has an orbit that connects a hyperbolic fixed point on one center manifold to a hyperbolic fixed point on the other. Then we prove some old and new results concerning the persistence of these connecting orbits and apply the results to find examples of systems in dimensions greater than three that possess Sil’nikov saddle-focus homoclinic orbits. Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, No. 1, pp. 28–55, January, 2008.     

A modification of the successive projections algorithm for spectral variable selection in the presence of unknown interferents

This work proposes a modification to the successive projections algorithm (SPA) aimed at selecting spectral variables for multiple linear regression (MLR) in the presence of unknown interferents not included in the calibration data set. The modified algorithm favours the selection of variables in which the effect of the interferent is less pronounced. The proposed procedure can be regarded as an adaptive modelling technique, because the spectral features of the samples to be analyzed are considered in the variable selection process. The advantages of this new approach are demonstrated in two analytical problems, namely (1) ultraviolet–visible spectrometric determination of tartrazine, allure red and sunset yellow in aqueous solutions under the interference of erythrosine, and (2) near-infrared spectrometric determination of ethanol in gasoline under the interference of toluene. In these case studies, the performance of conventional MLR-SPA models is substantially degraded by the presence of the interferent. This problem is circumvented by applying the proposed Adaptive MLR-SPA approach, which results in prediction errors smaller than those obtained by three other multivariate calibration techniques, namely stepwise regression, full-spectrum partial-least-squares (PLS) and PLS with variables selected by a genetic algorithm. An inspection of the variable selection results reveals that the Adaptive approach successfully avoids spectral regions in which the interference is more intense.     

General Melnikov Approach to Implicit ODE’s

Journal of Dynamics and Differential Equations - Existence of solutions connecting a singularity of a perturbed implicit differential equations is studied. It is assumed that the unperturbed...     

Electrical conductivity of the oxygen-deficient rutile CrNbO4−δ

Reduction of CrNbO₄ under 5% H₂/Ar at different temperatures has been carried out to obtain oxygen-deficient rutiles aiming for mixed ionic and electronic conductivities. Decomposition is observed at temperatures above 950 °C. Hence, the more reduced rutile that could be obtained corresponds to that obtained at 950 °C which has the composition CrNbO_3.96. When compared with CrNbO₄, the reduced product exhibits an electrical conductivity between three and four orders of magnitude higher. Both bulk and grain boundary conductivities are enhanced upon reduction. The small amount of vacancies generated by reduction does not induce oxygen conductivity. However, the presence of the corresponding small amount of Nb(IV) in the rutile affects strongly the electrical properties. This is likely related to the structural characteristics of rutile that allow for strong Nb–Nb interactions. On the other hand, no evidence of protonic conductivity has been found.     

Heteroclinic orbits in singular systems: A unifying approach

We consider singularly perturbed systems , such that=f(, _o, 0). _o ^m , has a heteroclinic orbitu(t). We construct a bifurcation functionG(, ) such that the singular system has a heteroclinic orbit if and only ifG(, )=0 has a solution=(). We also apply this result to recover some theorems that have been proved using different approaches.     

Heteroclinic period blow-up in certain symmetric ordinary differential equations

We consider the problem of bifurcation as well as of accumulation of periodic orbits on heteroclinic orbits for certain systems of ordinary differential equations either equivariant under finite groups of linear transformations or periodic in spatial variables.     

Bifurcation from heteroclinic orbits with semi-hyperbolic equilibria

Summary We study the problem of bifurcation from a heteroclinic orbit joining two semi-hyperbolic equilibrium points E₁ and E₂. We show that, if certain non-degeneracy assumptions are satisfied, E₁ and E₂ split into two equilibria E_ij, i,j= 1,2, and there are Melnikov-type conditions assuring the existence of a heteroclinic orbit from E_1i to E_2j, i,j=1,2 along directions that are tangent to the strongly-unstable (resp. strongly-stable) manifold of E_1j (resp. E_2j.Work performed under the auspicies of GNFM-CNR and within the activity of the group «Equazioni differenziali ordinarie e applicazioni»-MURST (Italy).     

Blue-emitting mesoporous films prepared via incorporation of luminescent Schiff base zinc(II) complex

Highly fluorescent materials have been prepared by incorporation of a zinc complex in mesoporous silica thin films with ordered pore structure. The zinc complex has been introduced into the mesoporous materials via impregnation in an ethanol solution. The incorporation into the films has been monitored by UV–Vis, Fourier transform infrared spectroscopy and spectroscopic ellipsometry. After 18 h of immersion in the doping solution the films showed strong blue emission, increase in the refractive index. Leaching experiments performed by immersing the samples in ethanol or tetrahydrofuran have shown that the chromophore is retained in the porous matrix.