Effects of nutrient enrichment on seagrass population dynamics: evidence and synthesis from the biomass-density relationships

The available data from experimental and descriptive studies on seagrass biomass and density responses to nutrient enrichment were analysed to assess the intraspecific mechanisms operating within seagrass populations and whether biomass-density relationships can provide relevant metrics for monitoring seagrasses. The response of shoot biomass and density to nutrient enrichment was dependent on the type of study; the short-term positive response of biomass and density in experimental studies reveals context-specific nutrient limitation of seagrasses. The long-term negative response of descriptive studies probably results from ecosystem-scale events related to nutrient enrichment such as increased turbidity, algal blooms, epiphyte loads and anoxia. Most seagrass species analysed lie in the nonthinning part of the theoretical biomass-density curves. A simultaneous increase in biomass and decrease in density, evidence of self-thinning, were only observed in 4 of 28 studies. The analysis of both the static and the dynamic biomass-density relationships revealed that the slopes increase under nutrient enrichment. Surprisingly, the species-specific slopes (log B-log D) were higher than one, revealing that the B/D ratio, that is, the average shoot biomass, increases with density in all seagrass species analysed. Nutrient enrichment further enhanced this effect as biomass-density slopes increased to even higher values. The main drivers behind the increasing biomass-density slopes under nutrient enrichment were the increase in shoot biomass at densities above a species-specific threshold and/or its decrease below that threshold. Synthesis. Contrasting short- and long-term responses of both biomass and density of seagrasses to nutrient enrichment suggest that the former, positive ones result from nutrient limitation, whereas the later, negative ones are mediated by whole ecosystem responses. In general, shoot biomass of seagrasses increases with density, and nutrient enrichment enhances this effect. Experimental testing of facilitation processes related to clonal integration in seagrasses needs to be done to reveal whether they determine the low incidence of self-thinning and the intriguing biomass-density relationships of seagrass species. The increasing slopes and decreasing intercepts of the species-specific dynamic biomass-density relationships of seagrasses and the decreasing coefficients of variation of both biomass and density constitute relevant, easy-to-collect metrics that may be used in environmental monitoring.EU project ECO-LAGUNES [SOE1/P2/F153]; COST Action [ES0906]; FCT [SFRH/BPD/37368/2007, SFRH/BPD/75307/2010]; NSERC PGSD; Killam Trustinfo:eu-repo/semantics/publishedVersio

First-principles study, fabrication and characterization of (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramic

The formation possibility of a new (Zr0.25Nb0.25Ti0.25V0.25)C high-entropy ceramic (ZHC-1) was first analyzed by the first-principles calculations and thermodynamical analysis and then it was successfully fabricated by hot pressing sintering technique. The first-principles calculation results showed that the mixing enthalpy of ZHC-1 was 5.526 kJ/mol and the mixing entropy of ZHC-1 was in the range of 0.693R-1.040R. The thermodynamical analysis results showed that ZHC-1 was thermodynamically stable above 959 K owing to its negative mixing Gibbs free energy. The experimental results showed that the as-prepared ZHC-1 (95.1% relative density) possessed a single rock-salt crystal structure, some interesting nanoplate-like structures and high compositional uniformity from nanoscale to microscale. By taking advantage of these unique features, compared with the initial metal carbides (ZrC, NbC, TiC and VC), it showed a relatively low thermal conductivity of 15.3 + - 0.3 W/(m.K) at room temperature, which was due to the presence of solid solution effects, nanoplates and porosity. Meanwhile, it exhibited the relatively high nanohardness of 30.3 + - 0.7 GPa and elastic modulus of 460.4 + - 19.2 GPa and the higher fracture toughness of 4.7 + - 0.5 MPa.m1/2, which were attributed to the solid solution strengthening mechanism and nanoplate pullout and microcrack deflection toughening mechanism.Comment: 49 pages,6 figures, 4 table

On the gravitational redshift

The study of the gravitational redshift\,---\,a relative wavelength increase of $\approx 2 \times 10^{-6}$ was predicted for solar radiation by Einstein in 1908\,---\,is still an important subject in modern physics. In a dispute whether or not atom interferometry experiments can be employed for gravitational redshift measurements, two research teams have recently disagreed on the physical cause of the shift. Regardless of any discussion on the interferometer aspect\,---\,we find that both groups of authors miss the important point that the ratio of gravitational to the electrostatic forces is generally very small. For instance, the gravitational force acting on an electron in a hydrogen atom situated in the Sun's photosphere to the electrostatic force between the proton and the electron is approximately $3 \times 10^{-21}$. A comparison of this ratio with the predicted and observed solar redshift indicates a discrepancy of many orders of magnitude. Here we show, with Einstein's early assumption of the frequency of spectral lines depending only on the generating ion itself as starting point, that a solution can be formulated based on a two-step process in analogy with Fermi's treatment of the Doppler effect. It provides a sequence of physical processes in line with the conservation of energy and momentum resulting in the observed shift and does not employ a geometric description. The gravitational field affects the release of the photon and not the atomic transition. The control parameter is the speed of light. The atomic emission is then contrasted with the gravitational redshift of matter-antimatter annihilation events.Comment: 19 Pages; 2 Table

Slowdown and splitting of gap solitons in apodized Bragg gratings

We study the motion of gap solitons in two models of apodized nonlinear fiber Bragg gratings (BGs), with the local reflectivity (LR) varying along the fiber. A single step of LR, and a periodic array of alternating steps with opposite signs (a "Bragg superstructure") are considered. A challenging possibility is to slow down and eventually halt the soliton by passing it through the step of increasing reflectivity, thus capturing a pulse of standing light. First, we develop an analytical approach, assuming adiabatic evolution of the soliton, and making use of the energy conservation and balance equation for the momentum. Comparison with simulations shows that the analytical approximation is quite accurate (unless the inhomogeneity is too steep): the soliton is either transmitted across the step or bounces back. If the step is narrow, systematic simulations demontrate that the soliton splits into transmitted and reflected pulses (splitting of a BG soliton which hits a chirped grating was observed in experiments). Moving through the periodic "superstructure", the soliton accummulates distortion and suffers radiation loss if the structure is composed of narrow steps. The soliton moves without any loss or irreversible deformation through the array of sufficiently broad steps.Comment: to appear in a special issue on Wave-Optical Engineering, Journal of Modern Optic

El valor percibido en webs de social commerce: Efectos sobre la lealtad del consumidor.

El estudio del comportamiento del consumidor en webs de social commerce está en auge, debido al gran crecimiento del sector en los últimos años. A pesar de ello, su comprensión se encuentra en su infancia, debido a la multitud de factores influyentes. Esta investigación, a través de la metodología del estímulo-organismo-respuesta, estudia qué papel tiene el valor percibido (O) por el consumidor, mediante el análisis de dos de sus principales antecedentes (calidad del sistema y del servicio) (S), así como de sus efectos sobre la lealtad (R). Los resultados obtenidos a partir de la aplicación de la técnica PLS a una muestra de 272 consumidores habituales de estas webs ponen de manifiesto la gran importancia que la calidad de la web tiene en la generación de valor en el consumidor, así como el rol clave de éste sobre las intenciones del consumidor tanto para volver a comprar como para recomendar.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Atom Interferometry tests of the isotropy of post-Newtonian gravity

We present a test of the local Lorentz invariance of post-Newtonian gravity by monitoring Earth's gravity with a Mach-Zehnder atom interferometer that features a resolution of about 8*10^(-9)g/Hz^(1/2), the highest reported thus far. Expressed within the standard model extension (SME) or Nordtvedt's anisotropic universe model, the analysis limits four coefficients describing anisotropic gravity at the ppb level and three others, for the first time, at the 10ppm level. Using the SME we explicitly demonstrate how the experiment actually compares the isotropy of gravity and electromagnetism.Comment: Added outlook, corrected typos; to appear in PRL. 4 pages, 3 figure