1,520 research outputs found
Derivation of a multilayer approach to model suspended sediment transport: application to hyperpycnal and hypopycnal plumes
We propose a multi-layer approach to simulate hyperpycnal and hypopycnal
plumes in flows with free surface. The model allows to compute the vertical
profile of the horizontal and the vertical components of the velocity of the
fluid flow. The model can describe as well the vertical profile of the sediment
concentration and the velocity components of each one of the sediment species
that form the turbidity current. To do so, it takes into account the settling
velocity of the particles and their interaction with the fluid. This allows to
better describe the phenomena than a single layer approach. It is in better
agreement with the physics of the problem and gives promising results. The
numerical simulation is carried out by rewriting the multi-layer approach in a
compact formulation, which corresponds to a system with non-conservative
products, and using path-conservative numerical scheme. Numerical results are
presented in order to show the potential of the model
A Study in Cuba of the Biology, Ecology and Agroecological Management of \u3cem\u3eHeteropsylla Cubana\u3c/em\u3e Crawford in \u3cem\u3eLeucaena Leucocephala\u3c/em\u3e (Lam.) de Wit
As a consequence of the increase in Leucaena leucocephala areas to counter the shortage of feed in Cuban cattle production, there is a risk of the development of Heteropsylla cubana Crawford (Hemiptera: Psyllidae) as a pest in silvopastoral systems with this legume. This psyllid is known to be the main phytophagous pest (Valenciaga, 2003), which produces damage in 95% of the apical region of branches. Since information on the identification and biology of a pest species is a necessary prerequisite for its management, a taxonomic, biological and ecological study was conducted to define Heteropsylla behaviour in Cuban conditions and elaborate the theoretical basis to propose management alternatives
Water insertion and combined interstitial-vacancy oxygen conduction in the layered perovskites La1.2Sr0.8−xBaxInO4+δ
Layered perovskites of K2NiF4-type consist of single octahedral sheets alternating with NaCl-type layers, containing a substantial interstitial space. Based on the parent LaSrInO4+δ oxide, the series of title compounds have been prepared and investigated as possible solid electrolytes for solid-oxide fuel cells (SOFC). A charge misbalance is created by departure from the La/Sr = 1 : 1 ratio, favoring the insertion of extra oxygen atoms. The oxygen diffusion is further favored by introducing large Ba2+ ions, expanding the unit-cell size. Surprisingly, the presence of basic Ba ions drives the spontaneous insertion of water molecules in the interstitial space, as unveiled by a neutron powder diffraction (NPD) study at RT. Moreover, H2O molecules are split within the structure with protons bonded to the axial oxygens of the InO6 octahedra, and with OH units occupying the interstitial space. Electrical Conductivity measurements were made. The dc conductivity was measured under different oxygen partial pressures for both Ba-doped compounds at 600 °C and 800 °C showing mixed ionic and p-type electronic behavior at different oxygen partial pressures but with conductivities of the order of ≈10−4 (S cm−1), far below the conductivities values of the oxide electrodes used in SOFCs. To analyze the nature of the majority charge carrier, ac impedance spectroscopy (IS) was applied. In the temperature range 500-900 °C, La1.2Sr0.6Ba0.2InO4+δ oxide exhibits a conductivity improvement with respect to La1.2Sr0.8InO4+δ. Temperature-dependent NPD data show at 600 °C and 800 °C the presence of oxygen vacancies at the axial octahedral positions as well as interstitial oxygen, favoring a mixed conduction mechanism for oxide ions, which may account for the enhancement of the transport properties. The present result endorses the validity of this design procedure and supports K2NiF4-related compounds as promising candidates for solid-oxide electrolytes.Fil: Troncoso, L.. Universidad Austral de Chile; ChileFil: Arce, Mauricio Damián. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa - Nodo Bariloche | Comisión Nacional de EnergÃa Atómica. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa - Nodo Bariloche; ArgentinaFil: Fernández DÃaz, M. T.. Institut Laue Langevin; FranciaFil: Mogni, Liliana Verónica. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa - Nodo Bariloche | Comisión Nacional de EnergÃa Atómica. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa. Unidad Ejecutora Instituto de Nanociencia y NanotecnologÃa - Nodo Bariloche; ArgentinaFil: Alonso, J. A.. Instituto de Ciencia de Materiales de Madrid; Españ
Microscopic transition potential: Determination of and coupling constants
A transition potential, based on an effective
quark-quark interaction and a constituent quark cluster model for baryons, is
derived in the Born-Oppenheimer approach. The potential shows significant
differences with respect to those obtained by a direct scaling of the
nucleon-nucleon interaction. From its asymptotic behavior we extract the values
of and coupling constants in a
particular coupling schemeComment: 15 eps figures, Accepted for publication in Phys. Rev.
Density and reproductive characteristics of female brown bears in the Cantabrian Mountains, NW Spain
Here we present annual nearest-neighbour distances (as a proxy of density) between females with cubs-of-the-year (hereafter FCOY) and reproductive characteristics of brown bears Ursus arctos in the Cantabrian Mountains (NW Spain), from 1989 to 2017. FCOY nearest-neighbour distances and reproduction parameters of 19 focal females followed over several consecutive years (from 2004 to 2017) were obtained from bears inhabiting the western sector of the Cantabrian Mountains, where most of the bear population resides. In contrast, general reproductive characteristics were studied in the whole Cantabrian Mountains (western and eastern sectors together) on a sample of 362 litter sizes and 695 cubs. Mean nearest-neighbour distance between FCOY was 2559 ± 1222 m (range = 1305–4757 m). Mean litter size was significantly larger in the west (1.8 ± 0.2 cubs) than in the east (1.3 ± 0.6 cubs). Mean litter size for the whole of the Cantabrian Mountains was 1.6 ± 0.3 cubs. Litter sizes of one, two and three cubs represented 33.4, 56.1 and 10.5% of observed family groups, respectively. Interannual variations in litter size were not significant for both the western and the eastern areas. Mean cub mortality was 0.2 ± 0.5 cubs and did not vary among years. Cub mortality per litter size was 3.9% for one cub, 69.2% for two cubs and 26.9% for three cubs. Mean reproductive rate of the 19 focal females was 1.5 ± 0.6 cubs (n = 58 litters). Litter size of focal FCOY did not differ from the litter size obtained from systematic observations in the whole Cantabrian Mountains. During this period, cub mortality occurred in 24.1% of the 58 litters. Females usually bred every second year (average litter interval = 2.2 years). The estimated reproductive rate for the bear population was 0.7 young born/year/reproductive adult female
SDSS IV MaNGA: Dependence of Global and Spatially Resolved SFR-M ∗ Relations on Galaxy Properties
Indexación: Scopus.The galaxy integrated Hα star formation rate-stellar mass relation, or SFR(global)-M ∗(global) relation, is crucial for understanding star formation history and evolution of galaxies. However, many studies have dealt with SFR using unresolved measurements, which makes it difficult to separate out the contamination from other ionizing sources, such as active galactic nuclei and evolved stars. Using the integral field spectroscopic observations from SDSS-IV MaNGA, we spatially disentangle the contribution from different Hα powering sources for ∼1000 galaxies. We find that, when including regions dominated by all ionizing sources in galaxies, the spatially resolved relation between Hα surface density (ΣHα(all)) and stellar mass surface density (Σ∗(all)) progressively turns over at the high Σ∗(all) end for increasing M ∗(global) and/or bulge dominance (bulge-to-total light ratio, B/T). This in turn leads to the flattening of the integrated Hα(global)-M ∗(global) relation in the literature. By contrast, there is no noticeable flattening in both integrated Hα(H ii)-M ∗(H ii) and spatially resolved ΣHα(H ii)-Σ∗(H ii) relations when only regions where star formation dominates the ionization are considered. In other words, the flattening can be attributed to the increasing regions powered by non-star-formation sources, which generally have lower ionizing ability than star formation. An analysis of the fractional contribution of non-star-formation sources to total Hα luminosity of a galaxy suggests a decreasing role of star formation as an ionizing source toward high-mass, high-B/T galaxies and bulge regions. This result indicates that the appearance of the galaxy integrated SFR-M ∗ relation critically depends on their global properties (M ∗(global) and B/T) and relative abundances of various ionizing sources within the galaxies.http://iopscience.iop.org/article/10.3847/1538-4357/aaa9bc/met
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