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Yttrium-doped barium zirconate (BZY), one of the protonic conductors considered to be used as solid electrolyte in solid oxide fuel cells (SOFC) operating at temperatures lower than the one found in conventional oxide-ion SOFCs, still presents some challenges to reach high density and high electrical conductivity: the difficulty to sinter at temperatures well below its melting point and the blocking of the conducting species at the grain boundaries. We describe an experimental sequence to prepare powders and to obtain highly dense BZY ceramic pellets with enhanced electrical conductivity, using either phosphor pentoxide (PO), boron oxide (BO) or zinc oxide (ZnO) as sintering aid. The reactions leading to sintering ceramic pellets with densities higher than 94% of the theoretical density and improved electrical performance are monitored by thermal analyses. BZY with the addition of 5 mass% PO or 2 mass% ZnO shows a tenfold enhancement of the electrical conductivity. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method to describe the many-body problem of electrons in honeycomb materials via the introduction of random fields which are coupled to the electrons and have a Gaussian distribution. From a one-body approach to the problem, after integrating exactly the contribution of the random fields, one builds a non-hermitian and dissipative effective Hamiltonian with two-body interactions. Our approach introduces besides the usual average over the electron field a second average over the random fields. The interplay of two averages enables the definition of various types of Green's functions which allow the investigation of fluctuation-dissipation characteristics of the interactions that are a manifestation of the many-body problem. In the current work, we study only the dissipative term, through the perturbative analysis of the dynamics associated the effective Hamiltonian generated by two different kinds of couplings. For the cases analyzed, the eigenstates of the effective Hamiltonian are complex and, therefore, some of the states have a finite life time. Moreover, we also investigate, in the mean field approximation, the most general parity conserving coupling to the random fields and compute the width of charge carriers Γ as a function of the Fermi energy E . The theoretical prediction for Γ( E ) is compared to the available experimental data for graphene. The good agreement between Γ and Γ suggests that description of the many-body problem associated to the electrons in honeycomb materials can indeed be done via the introduction of random fields. [ABSTRACT FROM AUTHOR]

We propose a mirror model for ordinary and dark matter that assumes a new SU(3) gauge group of transformations, as a natural extension of the Standard Model (SM). A close study of big bang nucleosynthesis, baryon asymmetries, cosmic microwave background bounds, galaxy dynamics, together with the Standard Model assumptions, help us to set a limit on the mass and width of the new gauge boson. The cross section for the elastic scattering of a dark proton by an ordinary proton is estimated and compare to the WIMP-nucleon experimental upper bounds. It is observed that all experimental bounds for the various cross sections can be accommodated consistently within the gauge model. We also suggest a way for direct detection of the new gauge boson via one example of a SM forbidden process: $e^{+} + p \rightarrow \mu ^{+} + X$ , where X=Λ or Λ. [ABSTRACT FROM AUTHOR]

We investigate the dynamics of a quantum system coupled linearly to Gaussian white noise using functional methods. By performing the integration over the noisy field in the evolution operator, we get an equivalent non-Hermitian Hamiltonian, which evolves the quantum state with a dissipative dynamics. We also show that if the integration over the noisy field is done for the time evolution of the density matrix, a gain contribution from the fluctuations can be accessed in addition to the loss one from the non-hermitian Hamiltonian dynamics. We illustrate our study by computing analytically the effective non-Hermitian Hamiltonian, which we found to be the complex frequency harmonic oscillator, with a known evolution operator. It leads to space and time localisation, a common feature of noisy quantum systems in general applications. [ABSTRACT FROM AUTHOR]

Our research involves the development of a pH-sensitive chitosan-tetraethyl orthosilicate interpenetrating polymer network (Chi-TEOS IPN) suitable for the introduction of ordered silica nanoparticles. The pH-sensitive properties of the IPN provide an innovative framework for ordered colloidal silica (SiO) films known as photonic crystals. The pH-sensitive properties of chitosan occur naturally due to its cationic polyelectrolyte structure; cross-linking with TEOS provides mechanical strength and incorporation of the silica photonic crystal provides a means of optical detection for a pH-driven expansion mechanism. Chitosan-tetraethyl orthosilicate-silica (Chi-TEOS-SiO) composites are formed through a three-step mechanism in which the silica photonic crystal and Chi-TEOS IPN hydrogel are synthesized separately and then combined to form the Chi-TEOS-SiO composite. The silica photonic crystals, IPN membranes and final composite structures were analysed separately through optical, mechanical and swelling studies. Through the successful fabrication of a Chi-TEOS-SiO composite we propose a membrane suitable for applications in environmental, chemical and biological sensing of pH. [ABSTRACT FROM AUTHOR]

The computation of the optical conductivity of strained and deformed graphene is discussed within the framework of quantum field theory in curved spaces. The analytical solutions of the Dirac equation in an arbitrary static background geometry for one dimensional periodic deformations are computed, together with the corresponding Dirac propagator. Analytical expressions are given for the optical conductivity of strained and deformed graphene associated with both intra and interbrand transitions. The special case of small deformations is discussed and the result compared to the prediction of the tight-binding model. [ABSTRACT FROM AUTHOR]

The number of citations received by authors in scientific journals has become a major parameter to assess individual researchers and the journals themselves through the impact factor. A fair assessment therefore requires that the criteria for selecting references in a given manuscript should be unbiased with regard to the authors or journals cited. In this paper, we assess approaches for citations considering two recommendations for authors to follow while preparing a manuscript: (i) consider similarity of contents with the topics investigated, lest related work should be reproduced or ignored; (ii) perform a systematic search over the network of citations including seminal or very related papers. We use formalisms of complex networks for two datasets of papers from the arXiv and the Web of Science repositories to show that neither of these two criteria is fulfilled in practice. By representing the texts as complex networks we estimated a similarity index between pieces of texts and found that the list of references did not contain the most similar papers in the dataset. This was quantified by calculating a consistency index, whose maximum value is one if the references in a given paper are the most similar in the dataset. For the areas of 'complex networks' and 'graphenes', the consistency index was only 0.11-0.23 and 0.10-0.25, respectively. To simulate a systematic search in the citation network, we employed a traditional random walk search (i.e. diffusion) and a random walk whose probabilities of transition are proportional to the number of the ingoing edges of the neighbours. The frequency of visits to the nodes (papers) in the network had a very small correlation with either the actual list of references in the papers or with the number of downloads from the arXiv repository. Therefore, apparently the authors and users of the repository did not follow the criterion related to a systematic search over the network of citations. Based on these results, we propose an approach that we believe is fairer for evaluating and complementing citations of a given author, effectively leading to a virtual scientometry. [ABSTRACT FROM AUTHOR]

The development of polymer-based photovoltaic devices brings the promise of low-cost and lightweight solar energy conversion systems. This technology requires new materials and device architectures with enhanced efficiency and lifetime, which depends on the understanding of charge-transport mechanisms. Organic films combined with electronegative nanoparticles may form systems with efficient dissociation of the photogenerated excitons, thus increasing the number of carriers to be collected by the electrodes. In this paper we investigate the steady-state photoconductive action spectra of devices formed by a bilayer of regio-regular poly(3-hexylthiophene) (RRP3HT) and TiO sandwiched between ITO and aluminum electrodes (ITO/TiO:RRP3HT/Al). Photocurrents were measured for distinct bias voltages with illumination from either side of the device. Heterojunction structures were prepared by spin coating a RRP3HT film on an already deposited TiO layer on ITO. Symbatic and antibatic curves were obtained and a model for photocurrent action spectra was able to fit the symbatic responses. The quantum yield increased with the electric field, indicating that exciton dissociation is a field-assisted process as in an Onsager mechanism. Furthermore, the quantum yield was significantly higher when illumination was carried out through the ITO electrode onto which the TiO layer was deposited, as the highly electronegative TiO nanoparticles were efficient in exciton dissociation. [ABSTRACT FROM AUTHOR]

The compatibility of the pure power law infrared solution of QCD and lattice data for the gluon and ghost propagators in Landau gauge is discussed. For the gluon propagator, the lattice data are well described by a pure power law with an infrared exponent κ∼0.53, in the Dyson–Schwinger notation. κ is measured using a technique that suppresses finite volume effects. This value is consistent with a vanishing zero momentum gluon propagator, in agreement with the Gribov–Zwanziger confinement scenario. For the ghost propagator, the lattice data seem not to follow a pure power law, at least for the range of momenta accessed in our simulation. [ABSTRACT FROM AUTHOR]

A generalized Cho-Faddeev-Niemi ansatz for SU(3) Yang-Mills is investigated. The corresponding classical field equations are solved for its simplest parametrization. From these solutions it is possible to define a confining non-relativistic central potential used to study heavy quarkonia. The associated spectra reproduces the experimental spectra with an error of less than 3% for charmonium and 1% for bottomonium. Moreover, the recently discovered new charmonium states can be accommodate in the spectra, keeping the same level of precision. The leptonic widths show good agreement with the recent measurements. The charmonium and bottomonium E1 electromagnetic transitions widths are computed and compared with the experimental values. [ABSTRACT FROM AUTHOR]

Thermal behavior of rare earth nitrate complexes with 2-azacyclononanone (AZA) with Ln(NO3)3·3(AZA) composition (where Ln=Gd, Er and Ho) was analyzed in kinetic point of view. Kinetic parameters were calculated from thermogravimetric data. All obtained results were similar. The first decomposition step was representative to the loss of ligand and the residue was essentially Ln2O3. Furthermore, a reaction path was proposed for the thermal decomposition of the Ln(NO3)3·3(AZA). [ABSTRACT FROM AUTHOR]

Examples of the application of k0 standardized instrumental neutron activation analysis (k0-INAA) to aerosols and biological monitors in the last 10 years at Instituto Tecnológico e Nuclear (ITN) are given. As an analytical technique, INAA, in association with the k0 method was applied to these materials in four different projects, aiming at monitoring concentrations of heavy metals and others elements in the atmosphere in the Portuguese territory. In these studies we analysed the lichen Parmelia sulcata Taylor and olive tree bark as monitors as well as aerosol samples. For each project some representative results are presented, followed by a discussion of the application of this technique to environmental studies. [ABSTRACT FROM AUTHOR]

A series of measurements were carried out to establish the reliability associated with isotope ratio (235/238) measurements on uranium samples using a quadrupole inductively coupled plasma mass spectrometer (ICPMS). Figures of merit related to the isotopic measurements were determined using non certified as well as certified materials provided by the New Brunswick Laboratory (NBL). The experimental results showed that repeatability is around 0.5% while reproducibility was calculated as 0.27%. Mass discrimination was determined as 0.03% per mass unit and the system linearity check over five orders of isotope ratios yielded a mass discrimination factor ( K factor) of 1.0002±0.0081 (0.81%, 2 s). The mean error of measurement obtained from six different certified reference materials was 0.77%. [ABSTRACT FROM AUTHOR]

A new thymocyte membrane-brain antigenic system is defined for the mouse and rat. Monoclonal antibody NIM-M129 recognizes a membrane antigen that has a similar size to Thy-1 (20-23 kd) but entirely different tissue distribution. It is absent from cortisone-resistant thymocytes, murine peripheral T cells, T-cell blasts, and T-cell lymphomas, or rat bone marrow. However, the determinant exhibits a quantitative difference in expression on thymocytes of Thy-1 (low) and Thy-1 (high) mice, with intermediate values for their F progeny. Backcross and F segregation tests between CBA and CBA- Thy-1 congenic lines established firm genetic linkage between Thy-1 and the level of epitope expression on the thymocyte cell surface. [ABSTRACT FROM AUTHOR]

An approximate dual representation for non-Abelian lattice gauge theories in terms of a new set of dynamical variables, the plaquette occupation numbers (PONs) that are natural numbers, is discussed. They are the expansion indices of the local series of the expansion of the Boltzmann factors for every plaquette of the Yang-Mills action. After studying the constraints due to gauge symmetry, the SU(2) gauge theory is solved using Monte Carlo simulations. For a PONs configuration the weight factor is given by Haar-measure integrals over all links whose integrands are products of powers of plaquettes. Herein, updates are limited to changes of the PON at a plaquette or all PONs on a coordinate plane. The Markov chain transition probabilities are computed employing truncated maximal trees and the Metropolis algorithm. The algorithm performance is investigated with different types of updates for the plaquette mean value over a large range of βs. Using a 124 lattice very good agreement with a conventional heath bath algorithm is found for the strong and weak coupling limits. Deviations from the latter being below 0.1% for 2.5<β<3. The mass of the lightest JPC=0++ glueball is evaluated and reproduces the results found in the literature. [ABSTRACT FROM AUTHOR]