Vertical segregation among pathways mediating nitrogen loss (N2 and N2O production) across the oxygen gradient in a coastal upwelling ecosystem

Indexación: ScopusThe upwelling system off central Chile (36.5 S) is seasonally subjected to oxygen (O2)-deficient waters, with a strong vertical gradient in O2 (from oxic to anoxic conditions) that spans a few metres (30-50€m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N2 and/or N2O, were studied using 15N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. Incubations were developed using water retrieved from the oxycline (25€m depth) and bottom waters (85€m depth) over the continental shelf off Concepción, Chile. Results of 15N-labelled incubations revealed higher N removal activity during the austral summer, with denitrification as the dominant N2-producing pathway, which occurred together with anammox at all times. Interestingly, in both spring and summer maximum potential N removal rates were observed in the oxycline, where a greater availability of oxygen was observed (maximum O2 fluctuation between 270 and 40€μmol€L'1) relative to the hypoxic bottom waters ( < €20€μmol€O2€L'1). Different pathways were responsible for N2O produced in the oxycline and bottom waters, with ammonium oxidation and dissimilatory nitrite reduction, respectively, as the main source processes. Ammonium produced by dissimilatory nitrite reduction to ammonium (DNiRA) could sustain both anammox and nitrification rates, including the ammonium utilized for N2O production. The temporal and vertical variability of /15N-NO3' confirms that multiple N-cycling processes are modulating the isotopic nitrate composition over the shelf off central Chile during spring and summer. N removal processes in this coastal system appear to be related to the availability and distribution of oxygen and particles, which are a source of organic matter and the fuel for the production of other electron donors (i.e. ammonium) and acceptors (i.e. nitrate and nitrite) after its remineralization. These results highlight the links between several pathways involved in N loss. They also establish that different mechanisms supported by alternative N substrates are responsible for substantial accumulation of N2O, which are frequently observed as hotspots in the oxycline and bottom waters. Considering the extreme variation in oxygen observed in several coastal upwelling systems, these findings could help to understand the ecological and biogeochemical implications due to global warming where intensification and/or expansion of the oceanic OMZs is projected.https://www.biogeosciences.net/14/4795/2017

Perturbation expansion for 2-D Hubbard model

We develop an efficient method to calculate the third-order corrections to the self-energy of the hole-doped two-dimensional Hubbard model in space-time representation. Using the Dyson equation we evaluate the renormalized spectral function in various parts of the Brillouin zone and find significant modifications with respect to the second-order theory even for rather small values of the coupling constant U. The spectral function becomes unphysical for $U \simeq W$, where W is the half-width of the conduction band. Close to the Fermi surface and for U<W, the single-particle spectral weight is reduced in a finite energy interval around the Fermi energy. The increase of U opens a gap between the occupied and unoccupied parts of the spectral function.Comment: 17 pages, 11 Postscript figures, Phys. Rev. B, accepte

A new triadotypomorphan insect from the Anisian (Middle Triassic), Buntsandstein facies, Spain

The species rubra sp. nov., a new triadotypomorphan insect from the Iberian Ranges, is described on the basis of a newly discovered specimen, found in fine grained sandstones of alluvial origin, in the lowermost part of the Eslida Formation (Buntsandstein facies), in the central part of the Iberian Ranges. The occurrence of a triadotypomorphan suggests an Anisian age of the Eslida Formation. The species represents the oldest Mesozoic insect described from Spain, and provides interesting information to better appreciate the process of ecosystems recovery after the Permian-Triassic boundary crisis.La especie rubra sp. nov., un nuevo insecto triadotipomorfo de la Cordillera Ibérica, es descrito en este trabajo en base a un nuevo espécimen hallado en un nivel de areniscas de grano fino de origen aluvial en la parte más baja de la Formación Eslida (facies Buntsandstein), en la zona central de la Cordillera Ibérica. La aparición de este triadotipomorfo confirma la edad Ansíense (Triásico Medio) de la Formación Eslida. La especie encontrada representa el insecto más antiguo hallado en el Mesozoico de España y una interesante información para comprender mejor el proceso de recuperación de los ecosistemas tras la crisis del límite Pérmico-Triásico

Dynamics of Electric Field Domains and Oscillations of the Photocurrent in a Simple Superlattice Model

A discrete model is introduced to account for the time-periodic oscillations of the photocurrent in a superlattice observed by Kwok et al, in an undoped 40 period AlAs/GaAs superlattice. Basic ingredients are an effective negative differential resistance due to the sequential resonant tunneling of the photoexcited carriers through the potential barriers, and a rate equation for the holes that incorporates photogeneration and recombination. The photoexciting laser acts as a damping factor ending the oscillations when its power is large enough. The model explains: (i) the known oscillatory static I-V characteristic curve through the formation of a domain wall connecting high and low electric field domains, and (ii) the photocurrent and photoluminescence time-dependent oscillations after the domain wall is formed. In our model, they arise from the combined motion of the wall and the shift of the values of the electric field at the domains. Up to a certain value of the photoexcitation, the non-uniform field profile with two domains turns out to be metastable: after the photocurrent oscillations have ceased, the field profile slowly relaxes toward the uniform stationary solution (which is reached on a much longer time scale). Multiple stability of stationary states and hysteresis are also found. An interpretation of the oscillations in the photoluminescence spectrum is also given.Comment: 34 pages, REVTeX 3.0, 10 figures upon request, MA/UC3M/07/9

Post-Eocene coupled oroclines in the Talesh (NW Iran): paleomagnetic constraints

The Talesh Mountains (NW Iran) witnessed a long deformation history from the Triassic Cimmerian orogeny to the ongoing Arabia-Eurasia collision. This protracted multi-stage deformation has generated a remarkably curved orogen with a puzzling kinematic and deformational history. In this study, we investigate the origin of the Talesh curvature through paleomagnetic analyses on rocks of Paleozoic, Mesozoic and Cenozoic age. Our results indicate that at least two major, large-scale, vertical-axis-rotations took place since the Late Cretaceous: 1) a pre-Eocene 73° ± 17° clockwise rotation and 2) post-Eocene differential rotations that formed the Z-shaped mountain belt within a crustal-scale shear zone. The latter involved an increasing amount of clockwise (CW) rotation from south (16°) to north (48°). The orocline formation likely started during the Oligocene where an approximately east-west oriented mountain belt was buckled by the Arabia-Eurasia collision, with Arabia acting as a rigid indenter and the South Caspian basin as a rigid backstop. We hypothesise that the NE-SW oriented Aras and Lahijan fault zones, inherited from transform faults related to the Mesozoic opening of the Caspian-Black Sea back-arc, accommodated the coupled orocline formation

Optimal phase response curves for stochastic synchronization of limit-cycle oscillators by common Poisson noise

We consider optimization of phase response curves for stochastic synchronization of non-interacting limit-cycle oscillators by common Poisson impulsive signals. The optimal functional shape for sufficiently weak signals is sinusoidal, but can differ for stronger signals. By solving the Euler-Lagrange equation associated with the minimization of the Lyapunov exponent characterizing synchronization efficiency, the optimal phase response curve is obtained. We show that the optimal shape mutates from a sinusoid to a sawtooth as the constraint on its squared amplitude is varied.Comment: 15 pages, 7 figure

A functional connection between translation elongation and protein folding at the ribosome exit tunnel in Saccharomyces cerevisiae

Proteostasis needs to be tightly controlled to meet the cellular demand for correctly de novo folded proteins and to avoid protein aggregation. While a coupling between translation rate and co-translational folding, likely involving an interplay between the ribosome and its associated chaperones, clearly appears to exist, the underlying mechanisms and the contribution of ribosomal proteins remain to be explored. The ribosomal protein uL3 contains a long internal loop whose tip region is in close proximity to the ribosomal peptidyl transferase center. Intriguingly, the rpl3[W255C] allele, in which the residue making the closest contact to this catalytic site is mutated, affects diverse aspects of ribosome biogenesis and function. Here, we have uncovered, by performing a synthetic lethal screen with this allele, an unexpected link between translation and the folding of nascent proteins by the ribosome-associated Ssb-RAC chaperone system. Our results reveal that uL3 and Ssb-RAC cooperate to prevent 80S ribosomes from piling up within the 5′ region of mRNAs early on during translation elongation. Together, our study provides compelling in vivo evidence for a functional connection between peptide bond formation at the peptidyl transferase center and chaperone-assisted de novo folding of nascent polypeptides at the solvent-side of the peptide exit tunnel

BCI-Based Navigation in Virtual and Real Environments

A Brain-Computer Interface (BCI) is a system that enables people to control an external device with their brain activity, without the need of any muscular activity. Researchers in the BCI field aim to develop applications to improve the quality of life of severely disabled patients, for whom a BCI can be a useful channel for interaction with their environment. Some of these systems are intended to control a mobile device (e. g. a wheelchair). Virtual Reality is a powerful tool that can provide the subjects with an opportunity to train and to test different applications in a safe environment. This technical review will focus on systems aimed at navigation, both in virtual and real environments.This work was partially supported by the Innovation, Science and Enterprise Council of the Junta de Andalucía (Spain), project P07-TIC-03310, the Spanish Ministry of Science and Innovation, project TEC 2011-26395 and by the European fund ERDF

Cluster diagonalization in systematically expanded Hilbert spaces: application to models of correlated electrons

A method of cluster diagonalization in a systematically expanded Hilbert space is described. We discuss some applications of this procedure to models of high-T_c superconductors, like the t - J and one and three bands Hubbard models in two dimensions. The results obtained with this method are compared against results obtained with other techniques dealing with truncated Hilbert spaces. The relation between this method of diagonalization in a reduced Hilbert space, and perturbation theory and variational techniques is also discussed.Comment: 26 pages + 12 figures, available upon request, LATEX, preprint ORNL/CCIP/93/

Disentangling environmental correlates of vascular plant biodiversity in a Mediterranean hotspot

We determined the environmental correlates of vascular plant biodiversity in the Baetic-Rifan region, a plant biodiversity hotspot in the western Mediterranean. A catalog of the whole flora of Andalusia and northern Morocco, the region that includes most of the Baetic-Rifan complex, was compiled using recent comprehensive floristic catalogs. Hierarchical cluster analysis (HCA) and detrended correspondence analysis (DCA) of the different ecoregions of Andalusia and northern Morocco were conducted to determine their floristic affinities. Diversity patterns were studied further by focusing on regional endemic taxa. Endemic and nonendemic alpha diversities were regressed to several environmental variables. Finally, semi-partial regressions on distance matrices were conducted to extract the respective contributions of climatic, altitudinal, lithological, and geographical distance matrices to beta diversity in endemic and nonendemic taxa. We found that West Rifan plant assemblages had more similarities with Andalusian ecoregions than with other nearby northern Morocco ecoregions. The endemic alpha diversity was explained relatively well by the environmental variables related to summer drought and extreme temperature values. Of all the variables, geographical distance contributed by far the most to spatial turnover in species diversity in the Baetic-Rifan hotspot. In the Baetic range, elevation was the most significant driver of nonendemic species beta diversity, while lithology and elevation were the main drivers of endemic beta diversity. Despite the fact that Andalusia and northern Morocco are presently separated by the Atlantic Ocean and the Mediterranean Sea, the Baetic and Rifan mountain ranges have many floristic similarities – especially in their western ranges – due to past migration of species across the Strait of Gibraltar. Climatic variables could be shaping the spatial distribution of endemic species richness throughout the Baetic-Rifan hotspot. Determinants of spatial turnover in biodiversity in the Baetic-Rifan hotspot vary in importance between endemic and nonendemic species