Formality in generalized Kähler geometry

We prove that no nilpotent Lie algebra admits an invariant generalized Kähler structure. This is done by showing that a certain differential graded algebra associated to a generalized complex manifold is formal in the generalized Kähler case, while it is never formal for a generalized complex structure on a nilpotent Lie algebra.     

Erratum to “Master equation for structured reservoirs” [Photonics Nanostruct.: Fundam. Appl. 2/3 (2004) 167]

In this work we generalize the formalism developed in our previous work [D. Mogilevtsev, S. Kilin, S.B. Cavalcanti, PNFA (2–3) (2004) 161]. We derive a master equation suitable to describe atom-field interaction in structured reservoirs, particulary those that exhibit ‘freezing’ of spontaneous decay as well as atom-field bound states. For a wide range of reservoir densities-of-states, this equation can be reduced to the Markovian form. In this work we extend the range of applicability of the method to times comparable to those of the atom-field bound state formation. We discuss novel features that such an extension brings forth and confirm predictions made in our previous work, namely, the stationary positive atomic inversion, a possibility of in-reservoir coherent control of the atom-field bound state and bipartite character of such a state in the absence of external perturbations.     

A variational approach of nonlinear dissipative pulse propagation

A variational technique to deal with nonlinear dissipative pulse propagation is established. By means of a generalization of the Kantorovitch method, suitable for non-conservative systems, we are able to cope with an extended nonlinear Schr?dinger equation (NLSE) which describes pulse propagation under the influence of nonlinear loss and/or gain, in particular, in the presence of two-photon absorption (TPA). Based on the characteristics of the exact solution of the NLSE in the absence of TPA, we investigate the effects of frequency dispersion of the nonlinear susceptibility associated to the two-photon resonance, obtaining the necessary conditions for a solitary wave solution, even in the presence of a self-steepening term. Received: 4 August 1997 / Received in final form: 25 November 1997 / Accepted: 14 January 1998     

Sunflower biodiesel

The higher is the degree of unsaturation in ester chain of a biodiesel, the smaller is its oxidation stability. Sunflower biodiesel obtained by the ethyl route possesses a high amount of unsaturated fatty acids, mainly oleic acid (C18:1) and linoleic acid (C18:2), thus being more prone to the oxidation process. In Brazil, with the purpose of meeting the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP), antioxidant additives, from synthetic and natural origins, have been added to the biofuel. Antioxidants are an alternative to prevent the oxidative deterioration of the fatty acid derivatives, as they are substances able to reduce the oxidation rate. In this study, the oxidative stability of sunflower biodiesel, obtained by the ethyl route and additivated with different concentrations of the antioxidants butylated hydroxytoluene (BHT) and t-butylhydroquinone (TBHQ), was evaluated by means of Pressure differential scanning calorimetry (P-DSC) and the Accelerated oxidative stability test (Rancimat, Method EN 14112). The results obtained by the two techniques showed the same oxidation tendency. Thus, P-DSC can be used as an alternative to determine the oxidative stability of biodiesel. The antioxidant TBHQ, added to biodiesel at the concentrations of 2000 and 2500 mg kg⁻¹, raised the oxidation induction time to a value higher than 6 h, the limit established by the Resolution ANP number 7/2008, thus being the best alternative among the studied antioxidants.     

Antioxidant capacity and phenolic content of Caesalpinia pyramidalis Tul. and Sapium glandulosum (L.) Morong from Northeastern Brazil

The aims of this study were to quantify the phenolic content and evaluate the antioxidant potential of extracts from the bark and leaves of C. pyramidalis and S. glandulosum. The total phenolic content (TPC) and total tannin content (TTC) were determined using the Folin-Ciocalteu method, and the total flavonoids content (TFC) was measured via complexation with aluminum chloride. The antioxidant activity was evaluated with DPPH (2.2-diphenyl-1-picrylhydrazyl) and FIC (ferrous ion chelating) assays. The TPC ranged between 135.55 ± 9.85 and 459.79 ± 11.65 tannic acid equivalents (TAE) in mg/g material (mg TAE/g). The leaves of both species contained high levels of tannins and flavonoids. The crude ethanol extracts (CEE) from the bark of C. pyramidalis showed high antioxidant activity when compared to ascorbic acid and rutin, whereas the CEE from the leaves was more efficient in chelating ferrous ions. C. pyramidalis had very high phenolic content and anti-radical activity, which indicates a need for further studies aimed at the purification and identification of compounds responsible for the antioxidant activity.     

The structure of the kinetoplast DNA network of Crithidia fasciculata revealed by atomic force microscopy

DNA is the biopolymer most studied by scanning probe methods, and it is now possible to obtain reliable and reproducible images of DNA using atomic force microscopy (AFM). AFM has been extensively used to elucidate morphological changes to DNA structure, such as the formation of knots, nicks, supercoiling and bends. The mitochondrial or kinetoplast DNA (kDNA) of trypanosomatids is the most unusual DNA found in nature, being unique in organization and replication. The kDNA is composed of thousands of topologically interlocked DNA circles that form a giant network. To understand the biological significance of the kinetoplast DNA, it is necessary to learn more about its structure. In the present work, we used two procedures to prepare kDNA networks of Crithidia fasciculata for observation by AFM. Because AFM allows for the examination of kDNA at high resolution, we were able to identify regions of overlapping kDNA molecules and sites where several molecules cross. This found support the earlier described kDNA structural organization as composed by interlocked circles. We also observed an intricate high-density height pattern around the periphery of the network of C. fasciculata, which appears to be a bundle of DNA fibers that organizes the border of the network. Our present data confirm that AFM is a powerful tool to study the structural organization of biological samples, including complex arrays of DNA such as kDNA, and can be useful in revealing new details of structures previously visualized by other means.     

An ideal gas approach to classify countries using financial indices

Traditionally, countries’ development is classified based on several features that can be related to economic and social factors. However, this classification task is costly due to the difficulty of obtaining those features. We propose a method to classify countries based on financial indices using an ideal gas model. The probability density function (pdf) of the return series of the financial indices is used to characterize the fluctuation of a market. Based on the pdf, the volatility and the B$B$ coefficient, which describe the behavior of world markets, are estimated. The evaluation procedure uses 34 indices from developed and developing countries. The results show that the proposed method is an accurate, fast and low-cost computational alternative to the classifications provided by traditional organizations.     

A fast method for the calculation of electron number density and temperature in laser-induced breakdown spectroscopy plasmas using artificial neural networks

A fast and precise method for the determination of electron temperature and electron number density in laser-induced plasmas is presented. The method is based on the use of a simple artificial neural network (ANN), trained on a suitable set of laser-induced breakdown spectroscopy spectra. The training procedure is quite fast; once the ANN is set, the determination of plasma temperature and electron number density is almost instantaneous, allowing the possibility of measuring these parameters, with good precision, in real time. A direct application of this new method could be the characterization of plasmas generated during pulsed laser deposition process of thin films and nanoparticles generation. The plasma electronic parameters will help to tune the energies involved in the stoichiometry and crystallization control of those nanostructured materials. As an example, the characteristics of the plasma induced by a Nd:YAG laser on a pure titanium target are determined, at different laser fluences.     

Exponential stability for the wave model with localized memory in a past history framework

In this paper we discuss the asymptotic stability as well as the well-posedness of the damped wave equation posed on a bounded domain Ω of ${\mathbb{R}}^n,n\ge 2$,

$\rho (x)u_{tt}?\mathrm{\Delta }u+\underset{0}{\overset{\infty }{\int }}g(s)\text{div}[a(x)\mathrm{?}u(?,t?s)]ds+b(x)u_t=0,$

subject to a locally distributed viscoelastic effect driven by a nonnegative function $a(x)$ and supplemented with a frictional damping $b(x)\ge 0$ acting on a region A of Ω, where $a=0$ in A. Assuming that $\rho (x)$ is constant, considering that the well-known geometric control condition $(\omega ,T_0)$ holds and supposing that the relaxation function g is bounded by a function that decays exponentially to zero, we prove that the solutions to the corresponding partial viscoelastic model decay exponentially to zero, even in the absence of the frictional dissipative effect. In addition, in some suitable cases where the material density $\rho (x)$ is not constant, it is also possible to remove the frictional damping term $b(x)u_t$, that is, the localized viscoelastic damping is strong enough to assure that the system is exponentially stable. The semi-linear case is also considered.     

Flag-dipole and flagpole spinor fluid flows in Kerr spacetimes

Flagpole and flag-dipole spinors are particular classes of spinor fields that has been recently used in different branches of theoretical physics. In this paper, we study the possibility and consequences of these spinor fields to induce an underlying fluid flow structure in the background of Kerr spacetimes. We show that flag-dipole spinor fields are solutions of the equations of motion in this context. To our knowledge, this is the second time that this class of spinor field appears as a physical solution, the first one occurring as a solution of the Dirac equation in ESK gravities.