Short report: Historical analysis of a near disaster: Anopheles gambiae in Brazil

Attributed to human-mediated dispersal, a species of the Anopheles gambiae complex invaded northeastern Brazil in 1930. This event is considered unique among the intercontinental introductions of disease vectors and the most serious one: ""Few threats to the future health of the Americas have equalled that inherent in the invasion of Brazil, in 1930, by Anopheles gambiae."" Because it was only in the 1960s that An. gambiae was recognized as a species complex now including seven species, the precise species identity of the Brazilian invader remains a mystery. Here we used historical DNA analysis of museum specimens, collected at the time of invasion from Brazil, and aimed at the identification of the Brazilian invader. Our results identify the arid-adapted Anopheles arabiensis as being the actual invading species. Establishing the identity of the species, in addition to being of intrinsic historical interest, can inform future threats of this sort especially in a changing environment. Furthermore, these results highlight the potential danger of human-mediated range expansions of insect disease vectors and the importance of museum collections in retrieving historical information.

Phylogenetic analysis of a near-full-length sequence of an erythrovirus genotype 3 strain isolated in Brazil

Human parvovirus B19 is the only member of the genus Erythrovirus that causes human disease. Recent findings of several strains with considerable sequence divergence from B19 have suggested a new classification for parvovirus genotypes as 1 (B19), 2 (A-6 and LaLi) and 3 (V9). In their overall DNA sequence, the three genotypes differ by similar to 10%. Here, we report the isolation of a genotype-3-related strain named BR543 during a prospective study conducted in Sao Paulo, Brazil. Analysis of the nearly full-length genome sequence of BR543 indicates that this B19 variant sequence clusters with Gh2768, a strain from Ghana belonging to subtype 3b, and showed mostly synonymous substitutions.

GEMINI near-infrared spectroscopic observations of young massive stars embedded in molecular clouds

K-band spectra of young stellar candidates in four Southern hemisphere clusters have been obtained with the Gemini Near-Infrared Spectrograph in Gemini South. The clusters are associated with IRAS sources that have colours characteristic of ultracompact H II regions. Spectral types were obtained by comparison of the observed spectra with those of a near-infrared (NIR) library; the results include the spectral classification of nine massive stars and seven objects confirmed as background late-type stars. Two of the studied sources have K-band spectra compatible with those characteristic of very hot stars, as inferred from the presence of C IV, N III and N V emission lines at 2.078, 2.116 and 2.100 mu m, respectively. One of them, I16177_IRS1, has a K-band spectrum similar to that of Cyg OB2 7, an O3If* supergiant star. The nebular K-band spectrum of the associated Ultra-Compact (UC) H II region shows the s-process [Kr III] and [Se IV] high excitation emission lines, previously identified only in planetary nebula. One young stellar object was found in each cluster, associated with either the main IRAS source or a nearby resolved Midecourse Space eXperiment (MSX) component, confirming the results obtained from previous NIR photometric surveys. The distances to the stars were derived from their spectral types and previously determined JHK magnitudes; they agree well with the values obtained from the kinematic method, except in the case of IRAS 15408-5356, for which the spectroscopic distance is about a factor of 2 smaller than the kinematic value.

Electronic and magnetic properties of Ti and Fe on graphene

The structural, electronic and magnetic properties of Fe and Ti atomic wires and the complete covering when adsorbed on graphene are presented through ab initio calculations based on density functional theory. The most stable configurations are investigated for Fe and Ti in different concentrations adsorbed on the graphene surface, and the corresponding binding energies are calculated. The results show a tendency of the Ti atoms to cover uniformly the graphene surface, whereas the Fe atoms form clusters. The adsorption of the transition metal on the graphene surface changes significantly the electronic density of states near the graphene Fermi region. In all arrangements studied, a charge transfer is observed from the adsorbed species to the graphene surface due to the high hybridizations between the systems.

MAGNETIC FIELD INDUCED NEAR-BAND-GAP OPTICAL PROPERTIES IN EuTe LAYERS

The magnetic response of the near-band-edge optical properties is studied in EuTe layers. In several magneto-optical experiments, the absorption and emission are described as well as the related Stokes shift. Specifically, we present the first experimental report of the photoluminescence excitation (PLE) spectrum in Faraday configuration. The PLE spectra shows to be related with the absorption spectra through the observation of resonance between the excitation light and the zero-field band-gap. A new emission line appears at 1.6 eV at a moderate magnetic field in the photoluminescence (PL) spectra. Furthermore, we examine the absorption and PL red-shift induced by the magnetic field in the light of the d-f exchange interaction energy involved in these processes. Whereas the absorption red-shift shows a quadratic dependence on the field, the PL red-shift shows a linear dependence which is explained by spin relaxation of the excited state.

Thymine hydroperoxide as a potential source of singlet molecular oxygen in DNA

The decomposition of organic hydroperoxides into peroxyl radicals is a potential source of singlet molecular oxygen [O(2) ((1)Delta(g))] in biological systems. This study shows that 5-(hydroperoxymethyl)uracil (5-HPMU), a thymine hydroperoxide within DNA, reacts with metal ions or HOCl, generating O(2) ((1)Delta(g)). Spectroscopic evidence for generation of O(2) ((1)Delta(g)) was obtained by measuring (i) the bimolecular decay, (ii) the monomolecular decay, and (iii) the observation of D(2)O enhancement of O(2) ((1)Delta(g)) production and the quenching effect of NaN(3). Moreover, the presence of O(2) ((1)Delta(g)) was unequivocally demonstrated by the direct characterization of the near-infrared light emission. For the sake of comparison, O(2) ((1)Delta(g)) derived from the H(2)O(2)/HOCl system and from the thermolysis of the N,N`-di(2,3-dihydroxypropyl)-1,4-naphthalenedipropanamide endoperoxide was also monitored. More evidence of O(2) ((1)Delta(g)) generation was obtained by chemical trapping of O(2) ((1)Delta(g)) with anthracene-9,10-divinylsulfonate (AVS) and detection of the specific AVS endoperoxide by HPLC/MS/MS. The detection by HPLC/MS of 5-(hydroxymethyl)uracil and 5-formyluracil, two thymine oxidation products generated from the reaction of 5-HPMU and Ce(4+) ions, supports the Russell mechanism. These photoemission properties and chemical trapping clearly demonstrate that the decomposition of 5-HPMU generates O(2) ((1)Delta(g)) by the Russell mechanism and point to the involvement of O(2) ((1)Delta(g)) in thymidine hydroperoxide cytotoxicity. (C) 2009 Elsevier Inc. All rights reserved.

Hydrogen adsorption on boron doped graphene: an ab initio study

(i) The electronic and structural properties of boron doped graphene sheets, and (ii) the chemisorption processes of hydrogen adatoms on the boron doped graphene sheets have been examined by ab initio total energy calculations. In (i) we find that the structural deformations are very localized around the boron substitutional sites, and in accordance with previous studies (Endo et al 2001 J. Appl. Phys. 90 5670) there is an increase of the electronic density of states near the Fermi level. Our simulated scanning tunneling microscope (STM) images, for occupied states, indicate the formation of bright (triangular) spots lying on the substitutional boron (center) and nearest-neighbor carbon (edge) sites. Those STM images are attributed to the increase of the density of states within an energy interval of 0.5 eV below the Fermi level. For a boron concentration of similar to 2.4%, we find that two boron atoms lying on the opposite sites of the same hexagonal ring (B1-B2 configuration) represents the energetically most stable configuration, which is in contrast with previous theoretical findings. Having determined the energetically most stable configuration for substitutional boron atoms on graphene sheets, we next considered the hydrogen adsorption process as a function of the boron concentration, (ii). Our calculated binding energies indicate that the C-H bonds are strengthened near boron substitutional sites. Indeed, the binding energy of hydrogen adatoms forming a dimer-like structure on the boron doped B1-B2 graphene sheet is higher than the binding energy of an isolated H(2) molecule. Since the formation of the H dimer-like structure may represent the initial stage of the hydrogen clustering process on graphene sheets, we can infer that the formation of H clusters is quite likely not only on clean graphene sheets, which is in consonance with previous studies (Hornekaer et al 2006 Phys. Rev. Lett. 97 186102), but also on B1-B2 boron doped graphene sheets. However, for a low concentration of boron atoms, the formation of H dimer structures is not expected to occur near a single substitutional boron site. That is, the formation (or not) of H clusters on graphene sheets can be tuned by the concentration of substitutional boron atoms.

Probing the (6,7)Li nucleon densities through a new break-up process approach

In this work we present a double folding optical model analysis of new near-barrier quasi-elastic experimental data for the (6,7)Li + (120)Sn systems. From the analysis, it was possible to confirm the ground-state nucleon densities assumed for the weakly bound (6,7)Li isotopes. The apparent discrepancies between the experimental densities and those based on Dirac-Hartree-Fock Bogoliubov (DHB) calculations were removed. A new approach that simulates the projectile break-up and a positive polarization from couplings of (6,7)Li bound states with the continuum was considered in the reaction mechanism. (C) 2010 Elsevier B.V. All rights reserved.