Ecological disturbance in tropical peatlands prior to marine Permian-Triassic mass extinction

The Permian-Triassic mass extinction is widely attributed to the global environmental changes caused by the eruption of the Siberian Traps. However, the precise temporal link between marine and terrestrial crises and volcanism is unclear. Here, we report anomalously high mercury (Hg) concentrations in terrestrial strata from southwestern China, synchronous with Hg anomalies in the marine Permian-Triassic type section. The terrestrial sediments also record increased abundance of fossil charcoal coincident with the onset of a negative carbon isotope excursion and the loss of tropical rainforest vegetation, both of which occurred immediately before the peak of Hg concentrations. The organic carbon isotope data show an ∼5‰–6‰ negative excursion in terrestrial organic matter (bulk organic, cuticles, and charcoal), reflecting change in atmospheric CO2 carbon-isotope composition coincident with enhanced wildfire indicated by increased charcoal. Hg spikes provide a correlative tool between terrestrial and marine records along with carbon isotope trends. These data demonstrate that ecological deterioration occurred in tropical peatlands prior to the main marine mass extinction

Spontaneous polarization and piezoelectric constants of III-V nitrides

The spontaneous polarization, dynamical Born charges, and piezoelectric constants of the III-V nitrides AlN, GaN, and InN are studied ab initio using the Berry phase approach to polarization in solids. The piezoelectric constants are found to be up 10 times larger than in conventional III-V's and II-VI's, and comparable to those of ZnO. Further properties at variance with those of conventional III-V compounds are the sign of the piezoelectric constants (positive as in II-VI's) and the very large spontaneous polarization.Comment: RevTeX 4 pages, improved upon revie

The pattern and timing of breathing during incremental exercise: a normative study

Clinical evaluation of the pattern and timing of breathing during submaximal exercise can be valuable for the identification of the mechanical ventilatory consequences of different disease processes and for assessing the efficacy of certain interventions.Sedentary individuals (60 male/60 female, aged 20-80 yrs) were randomly selected from >8,000 subjects and submitted to ramp incremental cycle ergometry. Tidal volume (V-T)/ resting inspiratory capacity, respiratory frequency, total respiratory time (Trot), inspiratory time (T-I), expiratory time (T-E), duty cycle (TI/Ttot) and mean inspiratory flow (V-T/T-I) were analysed at selected submaximal ventilatory intensities.Senescence and female sex were associated with a more tachypnoeic breathing pattern during isoventilation. the decline in T-tot was proportional to the TI and TE P reductions, i.e. T-I/T-tot was remarkably constant across age strata, independent of sex. the pattern, but not timing, of breathing was also influenced by weight and height; a set of demographically and anthropometrically based prediction equations are therefore presented.These data provide a frame of reference for assessing the normality of some clinically useful indices of the pattern and timing of breathing during incremental cycle ergometry in sedentary males and females aged 20-80 yrs.Universidade Federal de São Paulo, Pulmonary Funct & Clin Exercise Physiol Unit, Div Resp, Dept Med,Paulista Sch Med, BR-04020050 São Paulo, BrazilUniv Glasgow, Ctr Exercise Sci & Med, Inst Biol & Life Sci, Glasgow, Lanark, ScotlandUniversidade Federal de São Paulo, Pulmonary Funct & Clin Exercise Physiol Unit, Div Resp, Dept Med,Paulista Sch Med, BR-04020050 São Paulo, BrazilWeb of Scienc

Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials

Quantum ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). Quantum ESPRESSO stands for "opEn Source Package for Research in Electronic Structure, Simulation, and Optimization". It is freely available to researchers around the world under the terms of the GNU General Public License. Quantum ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively-parallel architectures, and a great effort being devoted to user friendliness. Quantum ESPRESSO is evolving towards a distribution of independent and inter-operable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.Comment: 36 pages, 5 figures, resubmitted to J.Phys.: Condens. Matte

Non-linear optical susceptibilities, Raman efficiencies and electrooptic tensors from first-principles density functional perturbation theory

The non-linear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach is based on the 2n + 1 theorem applied to an electric-field-dependent energy functional. We report the expressions for the calculation of the non-linear optical susceptibilities, Raman scattering efficiencies and electrooptic coefficients. Different formulations of third-order energy derivatives are examined and their convergence with respect to the k-point sampling is discussed. We apply our method to a few simple cases and compare our results to those obtained with distinct techniques. Finally, we discuss the effect of a scissors correction on the EO coefficients and non-linear optical susceptibilities

Density-Polarization Functional Theory of the response of a periodic insulating solid to an electric field.

The response of an infinite, periodic, insulating, solid to an infinitesimally small electric field is investigated in the framework of Density Functional Theory. We find that the applied perturbing potential is not a unique functional of the periodic density change~: it depends also on the change in the macroscopic {\em polarization}. Moreover, the dependence of the exchange-correlation energy on polarization induces an exchange-correlation electric field. These effects are exhibited for a model semiconductor. We also show that the scissor-operator technique is an approximate way of bypassing this polarization dependence.Comment: 11 pages, 1 Fig

Six-fold increase of atmospheric pCO2 during the Permian–Triassic mass extinction

The Permian–Triassic mass extinction was marked by a massive release of carbon into the ocean-atmosphere system, evidenced by a sharp negative carbon isotope excursion. Large carbon emissions would have increased atmospheric pCO2 and caused global warming. However, the magnitude of pCO2 changes during the PTME has not yet been estimated. Here, we present a continuous pCO2 record across the PTME reconstructed from high-resolution δ13C of C3 plants from southwestern China. We show that pCO2 increased from 426 +133/−96 ppmv in the latest Permian to 2507 +4764/−1193 ppmv at the PTME within about 75 kyr, and that the reconstructed pCO2 significantly correlates with sea surface temperatures. Mass balance modelling suggests that volcanic CO2 is probably not the only trigger of the carbon cycle perturbation, and that large quantities of 13C-depleted carbon emission from organic matter and methane were likely required during complex interactions with the Siberian Traps volcanism

Atomic structure and vibrational properties of icosahedral B4_4C boron carbide

The atomic structure of icosahedral B$_4$C boron carbide is determined by comparing existing infra-red absorption and Raman diffusion measurements with the predictions of accurate {\it ab initio} lattice-dynamical calculations performed for different structural models. This allows us to unambiguously determine the location of the carbon atom within the boron icosahedron, a task presently beyond X-ray and neutron diffraction ability. By examining the inter- and intra-icosahedral contributions to the stiffness we show that, contrary to recent conjectures, intra-icosahedral bonds are harder.Comment: 9 pages including 3 figures, accepted in Physical Review Letter

Theoretical study of O adlayers on Ru(0001)

Recent experiments performed at high pressures indicate that ruthenium can support unusually high concentrations of oxygen at the surface. To investigate the structure and stability of high coverage oxygen structures, we performed density functional theory calculations, within the generalized gradient approximation, for O adlayers on Ru(0001) from low coverage up to a full monolayer. We achieve quantitative agreement with previous low energy electron diffraction intensity analyses for the (2x2) and (2x1) phases and predict that an O adlayer with a (1x1) periodicity and coverage of 1 monolayer can form on Ru(0001), where the O adatoms occupy hcp-hollow sites.Comment: RevTeX, 6 pages, 4 figure