First Report on Rotenoids as Neurotoxic Principles of Seeds from Aeschynomene indica (Leguminosae)

Toxic principles from seeds of Aeschynomene indica collected in Brazil were analyzed. Dalpanol, 12 alpha-hydroxydalpanol and 11-hydroxydalpanol were identified using (1)H NMR in A. indica for the first time. 11-hydroxydalpanol has not been previously reported in the existing literature. Furthermore these rotenoids are likely the toxic principles that cause neurological signs in mice.

Unraveling effects of disorder on the electronic structure of SiO(2) from first principles

We present a first-principles systematic study of the electronic structure of SiO(2) including the crystalline polymorphs alpha quartz and beta cristobalite, and different types of disorder leading to the amorphous phase. We start from calculations within density functional theory and proceed to more sophisticated quasiparticle calculations according to the GW scheme. Our results show that different origins of disorder have also different impact on atomic and electronic-density fluctuations, which affect the electronic structure and, in particular, the size of the mobility gap in each case.

Quantum confinement effects on Mn-doped InAs nanocrystals: A first-principles study

We studied the effect of quantum confinement in Mn-doped InAs nanocrystals using theoretical methods. We observe that the stability of the impurities decreases with the size of the nanocrystals, making doping more difficult in small nanoparticles. Substitutional impurities are always more stable than interstitial ones, independent of the size of the nanocrystal. There is also a decrease in the energy difference between the high and low spin configurations, indicating that the critical temperature should decrease with the size of the nanoparticles, in agreement with experimental observations and in detriment to the development of functional spintronic devices with doped nanocrystals. Codoping with acceptors or saturating the nanocrystals with molecules that insert partially empty levels in the energy gap should be an efficient way to increase T(C).

Optical absorption and electronic band structure first-principles calculations of alpha-glycine crystals

Light absorption of alpha-glycine crystals grown by slow evaporation at room temperature was measured, indicating a 5.11 +/- 0.02 eV energy band gap. Structural, electronic, and optical absorption properties of alpha-glycine crystals were obtained by first-principles quantum mechanical calculations using density functional theory within the generalized gradient approximation in order to understand this result. To take into account the contribution of core electrons, ultrasoft and norm-conserving pseudopotentials, as well as an all electron approach were considered to compute the electronic density of states and band structure of alpha-glycine crystals. They exhibit three indirect energy band gaps and one direct Gamma-Gamma energy gap around 4.95 eV. The optical absorption related to transitions between the top of the valence band and the bottom of the conduction band involves O 2p valence states and C, O 2p conduction states, with the carboxyl group contributing significantly to the origin of the energy band gap. The calculated optical absorption is highly dependent on the polarization of the incident radiation due to the spatial arrangement of the dipolar glycine molecules; in the case of a polycrystalline sample, the first-principles calculated optical absorption is in good agreement with the measurement when a rigid energy shift is applied.

First-principles study of the adsorption of atomic and molecular hydrogen on BC(2)N nanotubes

The adsorption of atomic and molecular hydrogen on armchair and zigzag boron carbonitride nanotubes is investigated within the ab initio density functional theory. The adsorption of atomic H on the BC(2)N nanotubes presents properties which are promising for nanoelectronic applications. Depending on the adsorption site for the H, the Fermi energy moves toward the bottom of the conduction band or toward the top of the valence band, leading the system to exhibit donor or acceptor characteristics, respectively. The H(2) molecules are physisorbed on the BC(2)N surface for both chiralities. The binding energies for the H(2) molecules are slightly dependent on the adsorption site, and they are near to the range to work as a hydrogen storage medium.

Theory of nitride oxide adsorption on transition metal (111) surfaces: a first-principles investigation

In this work, we report a density functional theory study of nitric oxide (NO) adsorption on close-packed transition metal (TM) Rh(111), Ir(111), Pd(111) and Pt(111) surfaces in terms of adsorption sites, binding mechanism and charge transfer at a coverage of Theta(NO) = 0.25, 0.50, 0.75 monolayer (ML). Based on our study, an unified picture for the interaction between NO and TM(111) and site preference is established, and valuable insights are obtained. At low coverage (0.25 ML), we find that the interaction of NO/TM(111) is determined by an electron donation and back-donation process via the interplay between NO 5 sigma/2 pi* and TM d-bands. The extent of the donation and back-donation depends critically on the coordination number (adsorption sites) and TM d-band filling, and plays an essential role for NO adsorption on TM surfaces. DFT calculations shows that for TMs with high d-band filling such as Pd and Pt, hollow-site NO is energetically the most favorable, and top-site NO prefers to tilt away from the normal direction. While for TMs with low d-band filling (Rh and Ir), top-site NO perpendicular to the surfaces is energetically most favorable. Electronic structure analysis show that irrespective of the TM and adsorption site, there is a net charge transfer from the substrate to the adsorbate due to overwhelming back-donation from the TM substrate to the adsorbed NO molecules. The adsorption-induced change of the work function with respect to bare surfaces and dipole moment is however site dependent, and the work function increases for hollow-site NO, but decreases for top-site NO, because of differences in the charge redistribution. The interplay between the energetics, lateral interaction and charge transfer, which is element dependent, rationalizes the structural evolution of NO adsorption on TM(111) surfaces in the submonolayer regime.

Hybrid and multi-field variational principles for geometrically exact three-dimensional beams

This paper addresses the development of several alternative novel hybrid/multi-field variational formulations of the geometrically exact three-dimensional elastostatic beam boundary-value problem. In the framework of the complementary energy-based formulations, a Legendre transformation is used to introduce the complementary energy density in the variational statements as a function of stresses only. The corresponding variational principles are shown to feature stationarity within the framework of the boundary-value problem. Both weak and linearized weak forms of the principles are presented. The main features of the principles are highlighted, giving special emphasis to their relationships from both theoretical and computational standpoints. (C) 2010 Elsevier Ltd. All rights reserved.

Mendelian inheritance, linkage and linkage disequilibrium in microsatellite loci of Copaifera langsdorffii Desf.

Copaifera langsdorffii is a Neotropical tree with wide distribution in the Brazilian Atlantic rain forest and savanna. Although eight microsatellite loci (SSR) were developed in 2000 and have been widely used since then, there is yet no information about their inheritance, linkage and linkage disequilibrium (LD). Through the analysis of 28 open-pollinated (OP) progenies, the SSR loci revealed Mendelian inheritance and independent assortment. Using these progenies, young and adult trees LD was mainly detected in OP progenies. Our results show clear evidence that the eight SSR loci can be used without restriction in genetic diversity, mating system and parentage analysis.

Synchrotron X-ray imaging via ultra-small-angle scattering: principles of quantitative analysis and application in studying bone integration to synthetic grafting materials

Optimized experimental conditions for extracting accurate information at subpixel length scales from analyzer-based X-ray imaging were obtained and applied to investigate bone regeneration by means of synthetic beta-TCP grafting materials in a rat calvaria model. The results showed a 30% growth in the particulate size due to bone ongrowth/ingrowth within the critical size defect over a 1-month healing period.

Magnetism of Co overlayers and nanostructures on W(001): A first-principles study

The magnetic properties of Co nanostructures and a Co monolayer on W(001) have been studied in the framework of density functional theory. Different geometries such as planar and three-dimensional clusters have been considered, with cluster sizes varying between 2 and 13 atoms. The calculations were performed using the real-space linear muffin-tin orbital method (RS-LMTO-ASA). With respect to the stability of the magnetic state, we predict an antiferromagnetic (AFM) structure for the ground state of the planar Co clusters and a ferromagnetic (FM) state for the three-dimensional clusters. For the three-dimensional clusters, one of the AFM arrangements leads to frustration due to the competing FM and AFM exchange interactions between different atoms in the cluster, and gives rise to a non-collinear state with energy close to that of the FM ground state. The relative role of the Co-Co and Co-W exchange interactions is also investigated. (C) 2007 Elsevier B.V. All rights reserved.

First-principles calculation of the AlAs/GaAs interface band structure using a self-energy-corrected local density approximation

We apply a self-energy-corrected local density approximation (LDA) to obtain corrected bulk band gaps and to study the band offsets of AlAs grown on GaAs (AlAs/GaAs). We also investigate the Al(x)Ga(1-x)As/GaAs alloy interface, commonly employed in band gap engineering. The calculations are fully ab initio, with no adjustable parameters or experimental input, and at a computational cost comparable to traditional LDA. Our results are in good agreement with experimental values and other theoretical studies. Copyright (C) EPLA, 2011

Boron and nitrogen functionalized diamondoids: A first principles investigation

Chemically functionalized adamantane molecules have been investigated by first principles total energy calculations. Boron and nitrogen functionalized molecules were found to be very stable, consistent with available experimental data. Two hypothetical molecular crystals, involving functionalized adamantane, were investigated. These molecular crystals presented direct electronic bandgaps and large bulk moduli, which suggested a possible road for molecular self-assembly using functionalized diamondoids. (C) 2010 Elsevier B.V. All rights reserved.

Furan interaction with the Si(001)-(2 x 2) surface: structural, energetics, and vibrational spectra from first-principles

In this work we employ the state of the art pseudopotential method, within a generalized gradient approximation to the density functional theory, to investigate the adsorption process of furan on the silicon (001) surface. A direct comparison of different adsorption structures with x-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS), high resolution electron energy loss spectroscopy (HREELS), near edge x-ray absorption fine structure (NEXAFS), and high resolution spectroscopy experimental data allows us to identify the [4 + 2] cycloaddition reaction as the most probable adsorbate. In addition, theoretical scanning tunnelling microscopy (STM) images are presented, with a view to contributing to further experimental investigations.