Bubbling transition to spatial mode excitation in an extended dynamical system

We investigated the transition to spatio-temporal chaos in spatially extended nonlinear dynamical systems possessing an invariant subspace with a low-dimensional attractor. When the latter is chaotic and the subspace is transversely stable we have a spatially homogeneous state only. The onset of spatio-temporal chaos, i.e. the excitation of spatially inhomogeneous modes, occur through the loss of transversal stability of some unstable periodic orbit embedded in the chaotic attractor lying in the invariant subspace. This is a bubbling transition, since there is a switching between spatially homogeneous and nonhomogeneous states with statistical properties of on-off intermittency. Hence the onset of spatio-temporal chaos depends critically both on the existence of a chaotic attractor in the invariant subspace and its being transversely stable or unstable.     

A scenario for torus T destruction via a global bifurcation

We show a scenario of a two-frequency torus breakdown, in which a global bifurcation occurs due to the collision of a quasi-periodic torus T² with saddle points, creating a heteroclinic saddle connection. We analyze the geometry of this torus-saddle collision by showing the local dynamics and the invariant manifolds (global dynamics) of the saddle points. Moreover, we present detailed evidences of a heteroclinic saddle-focus orbit responsible for the type-II intermittency induced by this global bifurcation. We also characterize this transition to chaos by measuring the Lyapunov exponents and the scaling laws.     

Structural Determinants of the Specific Activities of an L-Amino Acid Oxidase from Pseudoalteromonas luteoviolacea CPMOR-1 with Broad Substrate Specificity

The Pseudoalteromonas luteoviolacea strain CPMOR-1 expresses a flavin adenine dinucleotide (FAD)-dependent L-amino acid oxidase (LAAO) with broad substrate specificity. Steady-state kinetic analysis of its reactivity towards the 20 proteinogenic amino acids showed some activity to all except proline. The relative specific activity for amino acid substrates was not correlated only with K_m or k_cat values, since the two parameters often varied independently of each other. Variation in K_m was attributed to the differential binding affinity. Variation in k_cat was attributed to differential positioning of the bound substrate relative to FAD that decreased the reaction rate. A structural model of this LAAO was compared with structures of other FAD-dependent LAAOs that have different substrate specificities: an LAAO from snake venom that prefers aromatic amino acid substrates and a fungal LAAO that is specific for lysine. While the amino acid sequences of these LAAOs are not very similar, their overall structures are comparable. The differential activity towards specific amino acids was correlated with specific residues in the active sites of these LAAOs. Residues in the active site that interact with the amino and carboxyl groups attached to the α-carbon of the substrate amino acid are conserved in all of the LAAOs. Residues that interact with the side chains of the amino acid substrates show variation. This provides insight into the structural determinants of the LAAOs that dictate their different substrate preferences. These results are of interest for harnessing these enzymes for possible applications in biotechnology, such as deracemization.     

Monopole and Coulomb Field as Duals within the Unifying Reissner–Nordstrm Geometry

We are going to prove that the Monopole and the Coulomb fields are duals within the unifying structure provided by the Reissner–Nordstr¨om spacetime. This is accomplished when noticing that in order to produce the tetrad that locally and covariantly diagonalizes the stress-energy tensor, both the Monopole and the Coulomb fields are necessary in the construction. Without any of them it would be impossible to express the tetrad vectors that locally and covariantly diagonalize the stress-energy tensor. Then, both electromagnetic fields are an integral part of the same structure, the Reissner–Nordstr¨om geometry.     

Observation of disruptions in tokamak plasma under the influence of resonant helical magnetic fields

Summary Disruptive instabilities were investigated in the small-tokamak TBR-1 during the application of resonant helical magnetic fields created by external helical windings. Indications were found that the main triggering mechanism of the disruption was the rapid increase of them=2/n=1 mode which, apparently after reaching a certain amplitude, interacts with other resistive modes: the internal 1/1 mode in the case of a major disruption, or with higherm components, as the 3/1 or 4/1, in the case of minor disruptions. After the coupling, the growth of the associated islands would create a chaotic field line distribution in the region between the corresponding rational magnetic surfaces which caused the gross particle transport and, finally, destroyed the confinement. In addition, investigations on higherZ _eff discharges in which a mixture of helium and hydrogen was used resulted in much more unstable plasmas but apparently did not alter the basic characteristics of the disruptions. The authors of this paper have agreed to not receive the proofs for correction.     

Onset of chaotic field line trajectories in tokamaks

Summary The onset of chaotic field line trajectories on tokamak plasmas perturbed by external resonant helical currents has been investigated. The spatial distribution of field lines is obtained integrating numerically the differential equations for the perturbed field lines and investigating the Poincaré maps characteristic of these fields. Several algorithms have been computed to identify the transition to large-scale stochasticity for this quasi-integrable dynamical system, which, for a given m.h.d. equilibrium, is determined by the enhancement of the coupling between the helical perturbation and the toroidicity, as the helical current increases. The authors of this paper have agreed to not receive the proofs for correction. Work partially supported by CNPq and FINEP.     

Polynomials versions of numerable type on non-archimedean locally convex spaces

The purpose of this article is to present some recent developments about polynomial conditions of denumerable type barrelledness between non-archimedean locally convex spaces over a non-trivially valued field of characteristic zero.     

INHIBITION OF DNA REPAIR AND PRODUCTION OF SINGLE-STRAND BREAKS IN ESCHERICHIA COLI BY REDUCTONE

Abstract— Reductone (HOCH₂COCHO), a keto-aldehyde produced by thermal degradation of some sugars, at alkaline pHs, blocks the excision repair of DNA lesions in uv-irradiated wild type Escherichia coli. This probably occurs as a result of inhibition of the exonucleolytic activity of DNA polymerase I. In addition, reductone alone induces DNA single-strand breaks. Repair of this damage is mainly dependent on the polA gene products.     

Photodynamic action of methylene blue: repair and mutation in Escherichia coli

The effects of the photodynamic action of methylene blue (MB-PDA) on strains of Escherichia coli were investigated to determine whether the dye could be used in photodynamic therapy (PDT). Using the method of alkaline sucrose gradient sedimentation, it was shown that in darkness MB induces a type of prelesion in DNA that transforms into single-strand breaks in alkaline conditions, provided that the dye is present during the processing of the gradient. This prelesion is completely reversible if the cells are washed immediately to remove the dye. However, after illumination with white light, the prelesions become "fixed" stable lesions, irreversible even after successive washings. The lethal damage induced by MB-PDA in E. coli can be repaired by the excision-repair system (about 30%) and by the recA-dependent repair system (about 70%). Polymerase I enzyme participates actively in the repair of the damage. MB-PDA is a weak mutagen and the induction of mutations by this treatment is restricted to high survival rates. Moreover, MB-PDA does not induce the SOS system (an inducible repair system dependent of the recA and loxA genes products), as measured by Weigle reactivation. However, it seems that this treatment can impair the repair systems in E. coli.     

Evaluation of alternate lines of Fe for sequential multi-element determination of Cu, Fe, Mn and Zn in soil extracts by high-resolution continuum source flame atomic absorption spectrometry

The usefulness of the secondary line at 252.744 nm and the approach of side pixel registration were evaluated for the development of a method for sequential multi-element determination of Cu, Fe, Mn and Zn in soil extracts by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS). The influence of side pixel registration on the sensitivity and linearity was investigated by measuring at wings (248.325, 248.323, 248.321, 248.329, and 248.332 nm) of the main line for Fe at 248.327 nm. For the secondary line at 252.744 nm or side pixel registration at 248.325 nm, main lines for Cu (324.754 nm), Mn (279.482 nm) and Zn (213.875 nm), sample flow-rate of 5.0 mL min⁻¹ and calibration by matrix matching, analytical curves in the 0.2-1.0 mg L⁻¹ Cu, 1.0-20.0 mg L⁻¹ Fe, 0.2-2.0 mg L⁻¹ Mn, 0.1-1.0 mg L⁻¹ Zn ranges were obtained with linear correlations better than 0.998. The proposed method was applied to seven soil samples and two soil reference materials (IAC 277; IAC 280). Results were in agreement at a 95% confidence level (paired t-test) with reference values. Recoveries of analytes added to soil extracts containing 0.15 and 0.30 mg L⁻¹ Cu, 7.0 and 14 mg L⁻¹ Fe, 0.60 and 1.20 mg L⁻¹ Mn, 0.07 and 0.15 mg L⁻¹ Zn, varied within the 94-99, 92-98, 93-101, and 93-103% intervals, respectively. The relative standard deviations (n = 12) were 2.7% (Cu), 1.4% (Fe - 252.744 nm), 5.7% (Fe - 248.325 nm), 3.2% (Mn) and 2.8% (Zn) for an extract containing 0.35 mg L⁻¹ Cu, 14 mg L⁻¹ Fe, 1.1 mg L⁻¹ Mn and 0.12 mg L⁻¹ Zn. Detection limits were 5.4 μg L⁻¹ Cu, 55 μg L⁻¹ Fe (252.744 nm), 147 μg L⁻¹ Fe (248.325 nm), 3.0 μg L⁻¹ Mn and 4.2 μg L⁻¹ Zn.