Photo-induced Fluorescence of Fluometuron in a Continuous-flow Multicommutation Assembly

This paper deals with the photo-induced fluorimetric determination of the herbicide Fluometuron with the aid of a continuous-flow assembly of the emergent and new methodology known as Multicommutation which was provided with an on-line photoreactor. Maximum fluorescence intensity was observed at basic pH solutions, 1×10⁻⁴ mol l⁻¹ NaOH, after 1.4 min of irradiation and being the maximum at λ_exc 247.0 nm and λ_em 325.0 nm. The influence of different experimental parameters either chemical (pH, surfactants presence, solvent polarity and temperature) or hydrodynamic (time of photo-degradation, size and number of different segments and flow-rate) was tested. The linear dynamic range was from 0.01 to 4.0 mg l⁻¹ of Fluometuron; the inter-day reproducibility (as R.S.D.) of the slope was 0.001% and 1.7% from the peaks intra-day reproducibility. A large series of potential interferents was studied and finally the method was applied to human urine, soil, formulation and water samples.     

Complete maximal surfaces in static Robertson–Walker 3-spaces

We construct a large family of complete maximal surfaces in the static Robertson–Walker 3-spaces with negative base curvature. These examples provide a wide variety of non-standard foliations of such spaces by entire maximal graphs.     

The heavy-ion magnetic spectrometer PRISMA

PRISMA is a magnetic spectrometer installed at Laboratori Nazionali di Legnaro (Italy) and designed for A=100–200, E=5–10 MeV-per-nucleon beams, and for possible use with the proposed radioactive beam facility SPES. The foremost features of the instrument are presented, along with the outline of two data analyses exemplifying the effectiveness of PRISMA-CLARA in studies of reaction dynamics.     

Electron microscopy characterization of nanostructured carbon obtained from chlorination of metallocenes and metal carbides

In this work we report some new well-defined carbon nanostructures produced by direct chlorination of metallocenes (ferrocene and cobaltocene) and NbC, at temperatures from 100 to 900 degrees C. Thus, amorphous carbon nanotubes with variable dimensions depending on reaction temperature were produced from ferrocene. When cobaltocene is the carbon precursor the main product are solid amorphous nanospheres. The high refractory metal carbide NbC as carbon source favours the growth of nanospherical cabbage-like particles with a higher degree of graphene sheets order. Besides, NbC crystallites encapsulated in an amorphous carbon shell were also found at lower temperatures (T< or =700 degrees C).     

Scalar-Particle Self-Energy Amplitudes and Confinement in Minkowski Space

We analyze the analytic structure of the Covariant Spectator Theory (CST) contribution to the self-energy amplitude for a scalar particle in a ${\phi^2\chi}$ theory. To this end we derive dispersion relations in 1+1 and in 3+1 dimensional Minkowski space. The divergent loop integrals in 3+1 dimensions are regularized using dimensional regularization. We find that the CST dispersion relations exhibit, in addition to the usual right-hand branch cut, also a left-hand cut. The origin of this “spectator” left-hand cut can be understood in the context of scattering for a scalar ${\phi^2\chi^2}$ -type theory. If the interaction kernel contains a linear confining component, its contribution to the self-energy vanishes exactly.     

Artificial intelligence in electrostatic risk management

In the last two decades protection against electrostatic hazards became a very important topic. The increase in the range of possible faults fast automated systems and complex fault analysis is required.The tools of artificial intelligence and expert systems have been applied successfully on this field and this paper aims to take a step further. While giving some insight to the currently used tools, another AI method, the 'support vector machines' are introduced in this paper. Besides a brief review on SVMs they are introduced to the SCOUT system, a novel approach to electrostatic hazard management.     

Characterization of NaTaO3 synthesized by ultrasonic method

NaTaO₃ perovskite-like materials were synthesized using sodium acetate and tantalum ethoxide as precursors in an ultrasonic bath at room temperature. The pristine sample was thermally treated at 600 °C and characterized using XRD, N₂ physisorption, DRS, SEM and TEM techniques. The structural characterization by X-ray powder diffraction revealed that the crystallization of the NaTaO₃ phase prepared at 600 °C showed agglomerates sizes in the micrometric scale, as confirmed by scanning electron microscopy (SEM). On the other hand, well-defined NaTaO₃ particles in the nanometric scale were determined using TEM. It was found that, for the treated sample, the band gap and BET area was 3.8 eV and 9.5 m² g^?1, respectively. The annealed perovskite, deposited onto ITO glass, presented an important variation in the open circuit potential transient during UV light irradiation in neutral solution, compared with its counterpart prepared by solid-state method. These intrinsic properties, given by the preparation route, might be appropriate for increase its photocatalytic activity.     

Electric field dependence of phase equilibria of binary Stockmayer fluid mixtures

A perturbation theory based study of the effect of an external electric field on the phase equilibrium properties of binary Stockmayer fluids is presented. The dipole–dipole interaction and the applied field are treated as independent perturbations to a Lennard–Jones mixture, and the reference fluid is treated by the van der Waals one-fluid approximation. A third-order free energy expression in the electric field strength is established, and the dielectric constant is calculated for a needle-shaped sample parallel to the field direction. We present and discuss vapour–liquid and liquid–liquid equilibrium curves at a given temperature for some dipolar mixtures exposed to an electric field, including chlorodifluoromethane +?difluoromethane and acetonitrile +?methanol. A sufficiently high electric field may result in massive shifts of vapour pressures and critical or azeotropic points, and can considerably alter the properties of coexisting phases. The vapour pressure decreases with increasing field strength.