Laser printing of enamels on tiles

A Nd:YAG laser beam is used as a tool to print patterns of coloured enamels on tile substrates. For this, the laser beam is scanned over a layer of raw enamel previously sprayed on the tile surface. The possibility to focus the laser energy to heat a small zone without affecting the rest of the piece presents some advantages in front of traditional furnace techniques in which the whole piece has to be heated; among them, energy saving and the possibility to apply enamels with higher melting temperatures than those of the substrate. In this work, we study the effects of laser irradiation of a green enamel, based in chromium oxide pigment and lead frit, deposited on a white tile substrate. Lines obtained with different combinations of laser beam power and scan speeds were investigated with the aim to optimize the process from the point of view of the quality of the patterns. For this purpose, the morphology of the lines and their cross-sections is studied. The results show that lines with good visual properties can be printed with the laser. The characteristics of the marked lines were found to be directly related with the accumulated energy density delivered. Moreover, there is a linear relationship between the accumulated energy density and the volume of melted material. A minimum accumulated energy density is required to melt a shallow zone of the glazed substrate to allow the adhesion of the enamelled lines.     

Magnetic dipole and electric quadrupole responses of elliptic quantum dots in magnetic fields

The magnetic dipole (M1) and electric quadupole (E2) responses of two-dimensional quantum dots with an elliptic shape are theoretically investigated as a function of the dot deformation and applied static magnetic field. Neglecting the electron-electron interaction we obtain analytical results which indicate the existence of four characteristic modes, with different B-dispersion of their energies and associated strengths. Interaction effects are numerically studied within the time-dependent local-spin-density and Hartree approximations, assessing the validity of the non-interacting picture. Received 29 November 2001 Published online 6 June 2002     

Density functional calculations for shell closures in Mg clusters

Motivated by recent measurements on Mg clusters we discuss the electronic structure and shell closures of these type of systems in the framework of self-consistent mean fields derived from density-functional theory. The ionic background is treated at different levels of refinement: spherical jellium model, and the spherically-averaged-pseudo-potential scheme (SAPS) with local as well as non-local pseudo-potentials. The ionic positions in SAPS are optimized using a Metropolis simulated annealing. It is shown that the details of ionic background influence sensitively the electronic levels sequence near the Fermi energy. In particular, the non-local effects from the pseudo-potential change the relations between states with high and with low angular momentum. Some of these effects go into the right direction towards experiment. Received 3 July 2001 and Received in final form 29 October 2001     

Potent "clicked" MMP2 inhibitors: synthesis, molecular modeling and biological exploration

A new series of MMP2 inhibitors is described, following a fragment-based drug design approach. One fragment containing an azide group and a well known hydroxamate Zinc Binding Group in a α-sulfone, α-tetrahydropyrane scaffold, has been synthesized. Water-LOGSY, STD and competition-STD experiments indicate that this fragment binds to the active site of the enzyme. A click chemistry reaction was used to connect the azide to lipophilic alkynes selected to interact selectively with the S1' subunit of MMP2, as shown by docking and molecular dynamic experiments of the designed compounds. The most potent compounds 18 and 19 displayed an IC(50) of 1.4 and 0.3 nM against MMP2 respectively, and showed negligible activity towards MMP1 and MMP7, two metalloproteinases which have a shallow S1' subsite. Compound 18 also showed a promising selectivity profile against some antitarget metalloproteinases, such as MMP8, and considerably less activity against MMP14 (IC(50) = 65 nM), and MMP9 (IC(50) = 98 nM), other MMPs characterized by having a deep S1' pocket and, therefore, more similar to MMP2.     

Pharmacognostic and acute toxicological evaluation of Scaptotrigona aff. postica propolis extract in pre-clinical assays

The propolis of Scaptotrigona aff. postica is popularly used in Maranh?o State, Brazil, for treating wounds and respiratory illnesses. Nevertheless, little is known about the chemical composition of this propolis and the adverse effects of its use. Hence, this study is a pharmacognostic characterisation of the propolis hydroalcoholic extract (PHE) from S. aff. postica. The methodology consisted of an evaluation of the sensory and chemical parameters. Chemical analysis of PHE indicated high concentrations of phenolic and triterpens substances, and the absence of steroids. Additionally, we evaluated the acute toxicity of propolis using 48 Swiss male and female mice. The animals received single doses of PHE (1000, 2000 or 4000 mg kg?1) orally and were observed for 14 days. After this period, the mice were sacrificed and the blood was used for biochemical and haematological evaluation. PHE did not induce any death, and the acute treatment significantly reduced serum concentrations of alanine aminotransferase and alkaline phosphatase. The resultant data indicate that PHE from S. aff. postica has low toxicity when used orally, even in high doses.     

Applicability of multisyringe chromatography coupled to cold-vapor atomic fluorescence spectrometry for mercury speciation analysis

In this paper, a novel automatic approach for the speciation of inorganic mercury (Hg(2+)), methylmercury (MeHg(+)) and ethylmercury (EtHg(+)) using multisyringe chromatography (MSC) coupled to cold-vapor atomic fluorescence spectrometry (CV/AFS) was developed. For the first time, the separation of mercury species was accomplished on a RP C18 monolithic column using a multi-isocratic elution program. The elution protocol involved the use of 0.005% 2-mercapthoethanol in 240 mM ammonium acetate (pH 6)-acetonitrile (99:1, v/v), followed by 0.005% 2-mercapthoethanol in 240 mM ammonium acetate (pH 6)-acetonitrile (90:10, v/v). The eluted mercury species were then oxidized under post-column UV radiation and reduced using tin(II) chloride in an acidic medium. Subsequently, the generated mercury metal were separated from the reaction mixture and further atomized in the flame atomizer and detected by AFS. Under the optimized experimental conditions, the limits of detection (3σ) were found to be 0.03, 0.11 and 0.09 μg L(-1) for MeHg(+), Hg(2+) and EtHg(+), respectively. The relative standard deviation (RSD, n=6) of the peak height for 3, 6 and 3 μg L(-1) of MeHg(+), Hg(2+) and EtHg(+) (as Hg) ranged from 2.4 to 4.0%. Compared with the conventional HPLC-CV/AFS hyphenated systems, the proposed MSC-CV/AFS system permitted a higher sampling frequency and low instrumental and operational costs. The developed method was validated by the determination of a certified reference material DORM-2 (dogfish muscle), and was further applied for the determination of mercury species environmental and biological samples.     

Optical, morphological and structural characterization of Langmuir-Schaefer films of a functionalized copper phthalocyanine

Langmuir-Schaefer (LS) films of copper(II) tetrakis-(isoprpoxy-carbonyl)-phthalocyanine (TiPCuPc) have been deposited onto various solid supports. Its floating film have been characterized at the air-water interface by means of Brewster Angle Microscopy and Langmuir curves. Vibrational modes of multilayer transferred LS film have been studied by Raman spectroscopy and the optical parameters (refractive index n and extinction coefficient k) have been determined in the visible range of the electromagnetic spectrum. Linearly polarized light absorbance measurements have been performed at room temperature in the 400-800 nm spectral range and the average orientation of the phthalocyanine rings have been estimated. Transmission electron microscopy has been also used to characterize the morphological properties of the LS film and a close packed arrangement of the deposited molecules has been observed.     

Thermal behavior of oxidation of TiN and TiC nanoparticles

Titanium nitride and carbide oxidation have been studied using TG and DSC. Titanium nitride shows a oxidation behavior were both techniques detect a unique phenomenon. Titanium carbide shows a variable behavior depending on the heating rate and sample size. Low masses and heating rates provide similar results to titanium nitride. However, using moderate sample sizes and scanning rates a two-stage oxidation is observed. The first step is extremely fast and exothermic, consuming the oxygen trapped inside the nanoparticle bed. The second is controlled by the diffusion of the oxygen and CO₂ through the sample. Thermal safety conclusions are extracted from this observation. Energies of activation calculated using traditional kinetic models are lower than those found in the literature, being an indication of the influence of the specific surface of the material.     

Multiple positive radial solutions on annuli for nonlinear Neumann problems with large growth

We consider a classical semilinear elliptic equation with Neumann boundary conditions on an annulus in R ^N . The nonlinear term is the product of a radially symmetric coefficient with a pure power. We prove that if the power is sufficiently large, the problem admits at least three distinct positive and radial solutions. In case the coefficient is constant, we show that none of the three solutions is constant. The methods are variational and are based on the study of a suitable limit problem.