Subatmospheric pressure in a water draining pipeline with an air pocket

[EN] An air pocket's behaviour inside of a pipeline during transient conditions is of great importance due to its effect on the safety of the hydraulic system and the complexity of modeling its behaviour. The emptying process from water pipelines needs more assessment because the generation of troughs of subatmospheric pressure may lead to serious damage. This research studies the air pocket parameters during an emptying process from a water pipeline. A well-equipped experimental facility was used to measure the pressure and the velocity change throughout the water emptying for different air pocket sizes and valve opening times. The phenomenon was simulated using a one-dimensional (1D) developed model based on the rigid formulation with a non-variable friction factor and a constant pipe diameter. The mathematical model shows good ability in predicting the trough of subatmospheric pressure value as the most important parameter which can affect the safety of hydraulic systems.This work was supported by the Fundacion CEIBA - Gobernacion de Bolivar, Colombia which covered the financial support for the doctoral student, Oscar E. Coronado-Hernandez.Coronado-Hernández, OE.; Fuertes-Miquel, VS.; Besharat, M.; Ramos, HM. (2018). Subatmospheric pressure in a water draining pipeline with an air pocket. Urban Water Journal. 15(4):1-7. https://doi.org/10.1080/1573062X.2018.1475578S1715

Coccolithophore biodiversity controls carbonate export in the Southern Ocean

Southern Ocean waters are projected to undergo profound changes in their physical and chemical properties in the coming decades. Coccolithophore blooms in the Southern Ocean are thought to account for a major fraction of the global marine calcium carbonate (CaCO3) production and export to the deep sea. Therefore, changes in the composition and abundance of Southern Ocean coccolithophore populations are likely to alter the marine carbon cycle, with feedbacks to the rate of global climate change. However, the contribution of coccolithophores to CaCO3 export in the Southern Ocean is uncertain, particularly in the circumpolar subantarctic zone that represents about half of the areal extent of the Southern Ocean and where coccolithophores are most abundant. Here, we present measurements of annual CaCO3 flux and quantitatively partition them amongst coccolithophore species and heterotrophic calcifiers at two sites representative of a large portion of the subantarctic zone. We find that coccolithophores account for a major fraction of the annual CaCO3 export, with the highest contributions in waters with low algal biomass accumulations. Notably, our analysis reveals that although Emiliania huxleyi is an important vector for CaCO3 export to the deep sea, less abundant but larger species account for most of the annual coccolithophore CaCO3 flux. This observation contrasts with the generally accepted notion that high particulate inorganic carbon accumulations during the austral summer in the subantarctic Southern Ocean are mainly caused by E. huxleyi blooms. It appears likely that the climate-induced migration of oceanic fronts will initially result in the poleward expansion of large coccolithophore species increasing CaCO3 production. However, subantarctic coccolithophore populations will eventually diminish as acidification overwhelms those changes. Overall, our analysis emphasizes the need for species-centred studies to improve our ability to project future changes in phytoplankton communities and their influence on marine biogeochemical cycles.info:eu-repo/semantics/publishedVersio

High-pressure phase transitions and compressibility of wolframite-type tungstates

This paper reports an investigation on the phase diagram and compressibility of wolframite-type tungstates by means of x-ray powder diffraction and absorption in a diamond-anvil cell and ab initio calculations. X-ray diffraction experiments show that monoclinic wolframite-type MgWO4 suffers at least two phase transitions, the first one being to a triclinic polymorph with a structure similar to that of CuWO4 and FeMoO4-II. The onset of each transition is detected at 17.1 and 31 GPa. In ZnWO4 the onset of the monoclinic-triclinic transition has been also found at 16.7 GPa. This transition does not involve any change in the atomic coordination as confirmed by x-ray absorption measurements. These findings are supported by density-functional theory calculations, which predict the occurrence of additional transitions upon further compression. Calculations have been also performed for wolframite-type MnWO4, which is found to have an antiferromagnetic configuration. In addition, our study reveals details of the local-atomic compression in MgWO4 and ZnWO4. In particular, below the transition pressure the ZnO6 and equivalent polyhedra tend to become more regular, whereas, the WO6 octahedra remain almost unchanged. Fitting the pressure-volume data we obtained the equation of state for the low-pressure phase of MgWO4 and ZnWO4. These and previous results on MnWO4 and CdWO4 are compared with the calculations. The compressibility of wolframite-type tungstates is also systematically discussed. Finally Raman spectroscopy measurements and lattice dynamics calculations are presented for MgWO4

Novel utility-scale photovoltaic plant electroluminescence maintenance technique by means of bidirectional power inverter controller

Nowadays, photovoltaic (PV) silicon plants dominate the growth in renewable energies generation. Utility-scale photovoltaic plants (USPVPs) have increased exponentially in size and power in the last decade and, therefore, it is crucial to develop optimum maintenance techniques. One of the most promising maintenance techniques is the study of electroluminescence (EL) images as a complement of infrared thermography (IRT) analysis. However, its high cost has prevented its use regularly up to date. This paper proposes a maintenance methodology to perform on-site EL inspections as efficiently as possible. First, current USPVP characteristics and the requirements to apply EL on them are studied. Next, an increase over the automation level by means of adding automatic elements in the current PV plant design is studied. The new elements and their configuration are explained, and a control strategy for applying this technique on large photovoltaic plants is developed. With the aim of getting on-site EL images on a real plant, a PV inverter has been developed to validate the proposed methodology on a small-scale solar plant. Both the electrical parameters measured during the tests and the images taken have been analysed. Finally, the implementation cost of the solution has been calculated and optimised. The results conclude the technical viability to perform on-site EL inspections on PV plants without the need to measure and analyse the panel defects out of the PV installation

Geoheritage as an educational resource and educational resources as heritage

El presente trabajo muestra una compilación de experiencias didácticas que emplean el patrimonio geológico como herramienta pedagógica en la enseñanza de las materias relacionadas con las Ciencias de la Tierra. El objetivo de todas ellas es acercar al alumnado al conocimiento y comprensión de los procesos que acontecen en nuestro planeta, con la finalidad de lograr un acercamiento y sensibilización hacia los mismos. Las seis propuestas seleccionadas presentan variedad en cuanto al contexto territorial de desarrollo de las actividades, a los contenidos y niveles trabajados (desde Enseñanza Secundaria hasta estudios universitarios) y a las metodologías utilizadas para la transmisión de dichos contenidos. Dentro de esta diversidad pueden distinguirse dos grupos de actividades diferentes. El primero de ellos se basa en el desarrollo de experiencias pedagógicas en localidades cuyas características geológicas resultan modélicas, únicas y/o espectaculares. Por el contrario, el segundo conjunto de actividades se centra en el trabajo de los recursos geológicos presentes en el entorno próximo del centro educativo. En ellas se explota su valor patrimonial, es decir, su potencial didáctico para abordar el estudio de la historia geológica del territorio. A través de las actividades incluidas en este compendio, se evidencia la validez de ambos tipos de aproximaciones y, al mismo tiempo, se debaten y realzan algunas de las virtudes más destacables de cada una de ellas. De esta manera, este catálogo podría resultar útil e inspirador para posibles planteamientos futuros.This manuscript presents a compilation of didactic experiences, which address the teaching of Earth Sciences through the knowledge of geological heritage. The aim of these proposals is to promote students’ comprehension of the Earth processes so that they may develop a positive attitude towards them. The six activities chosen offer a catalogue with a variety of sites, methodologies, contents and levels. Within this variety, the activities shown can be gathered into two separate groups. On the one hand, the first group collects experiences, which use geological heritage, i.e., the experiences are developed in places whose geological content is exemplary, unique and/or spectacular. On the other hand, the second group is focused on the geologic resources in the neighborhood of the school. These sites have heritage value, that is, an educational value for studying the geologic history of their territory. The activities drawn together show that both viewpoints are useful, and the benefits of each are pointed out. Consequently, this catalogue might be useful and inspiring for forthcoming attempts in this field

Optical and structural study of the pressure-induced phase transition of CdWO4

The optical absorption of CdWO4 is reported at high pressures up to 23 GPa. The onset of a phase transition was detected at 19.5 GPa, in good agreement with a previous Raman spectroscopy study. The crystal structure of the high-pressure phase of CdWO4 was solved at 22 GPa, employing single-crystal synchrotron x-ray diffraction. The symmetry changes from space group P2/c in the low-pressure wolframite phase to P21/c in the high-pressure postwolframite phase accompanied by a doubling of the unit-cell volume. The octahedral oxygen coordination of the tungsten and cadmium ions is increased to [7]-fold and [6+1]-fold, respectively, at the phase transition. The compressibility of the low-pressure phase of CdWO4 has been reevaluated with powder x-ray diffraction up to 15 GPa, finding a bulk modulus of B0=123 GPa. The direct band gap of the low-pressure phase increases with compression up to 16.9 GPa at 12 meV/GPa. At this point an indirect band gap crosses the direct band gap and decreases at −2 meV/GPa up to 19.5 GPa where the phase transition starts. At the phase transition the band gap collapses by 0.7 eV and another direct band gap decreases at –50 meV/GPa up to the maximum measured pressure. The structural stability of the postwolframite structure is confirmed by ab initio calculations, finding the postwolframite-type phase to be more stable than the wolframite at 18 GPa. Lattice dynamic calculations based on space group P21/c explain well the Raman-active modes previously measured in the high-pressure postwolframite phase. The pressure-induced band gap crossing in the wolframite phase as well as the pressure dependence of the direct band gap in the high-pressure phase are further discussed with respect to the calculations

Experimental and Theoretical Study of Bi2O2Se Under Compression

We report a joint experimental and theoretical study of the structural, vibrational, elastic, optical, and electronic properties of the layered high-mobility semiconductor Bi2O2Se at high pressure. A good agreement between experiments and ab initio calculations is observed for the equation of state, the pressure coefficients of the Raman-active modes and the bandgap of the material. In particular, a detailed description of the vibrational properties is provided. Unlike other Sillén-type compounds which undergo a tetragonal to collapsed tetragonal pressure-induced phase transition at relatively low pressures, Bi2O2Se shows a remarkable structural stability up to 30 GPa; however, our results indicate that this compound exhibits considerable electronic changes around 4 GPa, likely related to the progressive shortening and hardening of the long and weak Bi–Se bonds linking the Bi2O2 and Se atomic layers. Variations of the structural, vibrational, and electronic properties induced by these electronic changes are discussed

High-pressure structural and vibrational properties of monazite-type BiPO4, LaPO4, CePO4, and PrPO4

[EN] Monazite-type BiPO4, LaPO4, CePO4, and PrPO4 have been studied under high pressure by ab initio simulations and Raman spectroscopy measurements in the pressure range of stability of the monazite structure. A good agreement between experimental and theoretical Raman-active mode frequencies and pressure coefficients has been found which has allowed us to discuss the nature of the Raman-active modes. Besides, calculations have provided us with information on how the crystal structure is modified by pressure. This information has allowed us to determine the equation of state and the isothermal compressibility tensor of the four studied compounds. In addition, the information obtained on the polyhedral compressibility has been used to explain the anisotropic axial compressibility and the bulk compressibility of monazite phosphates. Finally, we have carried out a systematic discussion on the high-pressure behavior of the four studied phosphates in comparison to results of previous studies.The authors are thankful for the financial support to this research from the Spanish Ministerio de Economia y Competitividad, the Spanish Research Agency, and the European Fund for Regional Development under Grant Nos: MAT2016-75586-C4-1-P/2-P/3-P and MAT2015-71070-REDC. AM and PR-H acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster.Errandonea, D.; Gomis, O.; Rodríguez Hernández, P.; Muñoz, A.; Ruiz Fuertes, J.; Gupta, M.; Achary, S.... (2018). High-pressure structural and vibrational properties of monazite-type BiPO4, LaPO4, CePO4, and PrPO4. Journal of Physics Condensed Matter. 30(6). https://doi.org/10.1088/1361-648X/aaa20dS30