Spin-singlet clusters in the ladder compound NaV2O5

The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton.     

Dependence of pulser driving responses on electrical and motional characteristics of NDE ultrasonic probes

Acoustic performance in ultrasonic transmitters can be improved by means of a suitable electrical driving response and matching/tuning networks. It is important to predict this electrical response, but doing so is not easy because it departs notably from the nominal pattern with the loading probes. In practice, the analysis of HV pulser spikes in NDE applications requires fairly complex models in the transient regime and, in addition, non-linear problems could arise, especially in the case of tuned transmitters. In this paper, the most relevant influences of loading characteristics of NDT ultrasonic probes on the pulser electrical driving responses are evaluated in time and frequency domains. Conventional pulse generators and typical NDE pulsers are considered. Driving responses are analysed across commercial ultrasonic probes and, alternatively, across similar purely electrical loads. Distinct influences on pulser responses from electrical and motional sections of the probes are identified. All these aspects are studied on the basis of experimental and computer results.     

Two-phase electrohydrodynamic simulations using a volume-of-fluid approach

A numerical methodology to simulate two-phase electrohydrodynamic flows under the volume-of-fluid paradigm is proposed. The electric force in such systems acts only at the interface and is zero elsewhere in the two fluids. Continuum surface force representations are derived for the electric field force in a system of dielectric–dielectric and conducting–conducting fluids. On the basis of analytical calculations for simple flow problems we propose a weighted harmonic mean interpolation scheme to smoothen the electric properties in the diffused transition region (interface). It is shown that a wrong choice of interpolation scheme (weighted arithmetic mean) may lead to a transition region thickness dependent electric field in the bulk. We simulate a set of problems with exact or approximate analytical solutions to validate the numerical model proposed. A coupled level set and volume-of-fluid (CLSVOF) algorithm has been used for simulations presented here.     

Determination of glyphosate and its metabolites in plant material by reversed‐polarity CE with indirect absorptiometric detection

A simple CE method for simultaneous determination of glyphosate and its metabolites (i.e. aminomethylphosphonic acid, glyoxylate, sarcosine and formaldehyde) in plants is reported here. A BGE of pH 7.5, 10% ACN, 7.5 mM phthalate, containing 0.75 mM hexadecyltrimethylammonium bromide as an electro‐osmotic flow modifier, an applied voltage of –20 kV and absorptiometric monitoring at 220 nm were the optimal chemical and instrumental parameters. The method, with development time 20 min, shows linear calibrations within the range 5–500 μg/mL (for all target analytes) with correlation coefficients between 0.999 and 0.998. It has been validated by application to samples of Lolium spp. The electroinjection mode hinders most interferents to enter the capillary, thus providing a clean electropherogram and making unnecessary long sample‐preparation steps.     

Nonlinear age-dependent diffusive equations: A bifurcation approach

The main goal of this paper is the study of the existence and uniqueness of positive solutions of some nonlinear age-dependent diffusive models, arising from dynamic populations. We use a bifurcation method, for which it has been necessary to study in detail the linear and eigenvalue problems associated to the nonlinear problem in an appropriate space.     

On a Two-Variable Class of Bernstein–Szegő Measures

The one-variable Bernstein–Szegő theory for orthogonal polynomials on the real line is extended to a class of two-variable measures. The polynomials orthonormal in the total degree ordering and the lexicographical ordering are constructed and their recurrence coefficients discussed.      

Pentaquark Masses and Magnetic Moments in a Quark Cluster Approach

We study the stability of the different quark substructures in a quark cluster approach to pentaquark states considering the color-magnetic spin-spin interactions between quarks. The most likely configuration is found to be a triquark-diquark one where the two clusters are in a relative p-wave, the two quarks of the diquark are coupled to spin zero and anti-triplet representations of flavor and color, and the triquark has spin ? and belongs to the triplet representation of color and to the anti-sextet of flavor. Using this configuration we estimate the masses and magnetic moments of pentaquarks. Finally the calculation of the masses has been extended to some charmed pentaquarks.     

Fourier transform Raman and DFT study of three annulated oligothiophenes with different molecular shapes.

Herein, we study the conjugation properties of three different thienoacenes, each of which has three or four fused thiophene rings, by means of Fourier transform Raman spectroscopy. The B3LYP/6-31G** vibrational analysis of all of the collected spectroscopic data evidences that the selective enhancement of a limited number of Raman scatterings is related to the occurrence in the three thienoacenes of a vibronic coupling between the lowest unoccupied frontier molecular orbital (LUMO) and some Raman-active skeletal nu(C==C) stretching modes of 1600-1300 cm(-1).     

Influence of the Oxide Content in the Catalytic Power of Raney Nickel in Hydrogen Generation

The influence of oxides in the hydrogen evolution on Raney nickel electrocatalysts was characterized by electrochemical impedance measurements. In addition, these materials show competitive overpotentials for hydrogen evolution with a modified Watts bath as a binder for the Raney nickel. The optimum result was ?190?mV of overpotential at 100?mA?cm^?2. Oxygen in the Raney Ni catalyst affects its electroactivity toward hydrogen evolution. The source of oxygen is related to the presence of chloride ions in the modified Watts bath. A Watts bath binds Raney Ni particles to the surface of the catalysts and chloride regulates the oxygen content in the nickel binder during electrodeposition. High oxygen content increases the hydrogen evolution overpotential of the electrode. The electroactivity of the synthesized porous coatings was evaluated by polarization curves and impedance plots. In addition, surface characterization by X-ray diffraction, field emission–scanning electron microscopy equipped with energy-dispersive analysis, and X-ray photoelectron spectroscopy is reported.