1,871 research outputs found
LA CONSTRUCCIÓN DE LA ARQUITECTURA ORGANIZATIVA EN LAS ENTIDADES SIN FINES DE LUCRO. EL CASO DE LAS ONGD EN ESPAÑA
RESUMENEl objetivo del presente trabajo es valorar el equilibrio de las fuerzas organizativas en la construcción de una arquitectura organizativa eficiente y, todo ello, bajo un enfoque de agencia. Los resultados del análisis empírico, llevado a cabo en las más importantes ONGD españolas durante el año 2003, ponen de relieve la gran importancia de la influencia mutua de la delegación de derechos de decisión, sistemas de incentivos y el uso de medidas de evaluación del rendimiento en el logro del equilibrio organizativo, lo que nos permite afirmar que, para el caso estudiado, la teoría se confirma.ABSTRACTThe aim of this paper is to evaluate the balance of organizational components in the design of an efficient organizational architecture from an agency perspective. The results of the empirical analysis, performed in the most prominent Spanish NGDO throughout the year 2003, show the great importance of the mutual influence among the delegation of decision rights, the incentive systems and the use of performance measurements in the achievement of organizational equilibrium
Review and comparison of effective delayed neutron fraction calculation methods with Monte Carlo codes
The calculation of the effective delayed neutron fraction, beff , with Monte Carlo codes is a complex task due to the requirement of properly considering the adjoint weighting of delayed neutrons. Nevertheless, several techniques have been proposed to circumvent this difficulty and obtain accurate Monte Carlo results for beff without the need of explicitly determining the adjoint flux. In this paper, we make a review of some of these techniques; namely we have analyzed two variants of what we call the k-eigenvalue technique and other techniques based on different interpretations of the physical meaning of the adjoint weighting. To test the validity of all these techniques we have implemented them with the MCNPX code and we have benchmarked them against a range of critical and subcritical systems for which either experimental or deterministic values of beff are available. Furthermore, several nuclear data libraries have been used in order to assess the impact of the uncertainty in nuclear data in the calculated value of beff
Comparación entre las técnicas AEOS, Re-Mi y PS-logging aplicadas en un terreno de estructura profunda conocida
En este estudio se contrastan los resultados que ofrecen dos técnicas de uso habitual en el Laboratorio de Geotecnia del CEDEX, el AEOS y el PS-logging, con los de una técnica relativamente novedosa, el Re-Mi (o sísmica pasiva). Para ello se emplean los resultados obtenidos por las tres técnicas en un emplazamiento común de estructura profunda conocida: un tramo de terraplén ferroviario recién construido. La técnica más precisa en la identificación de las diferentes partes de la estructura de tierras (terraplén, cimiento y contacto con el terreno natural) es el PS-logging, seguido por el AEOS y Re-Mi. Los valores de Vs promedio proporcionados por cada técnica presentan importantes diferencias, obteniéndose los más altos con el PS-logging, seguido por AEOS y Re-Mi. La desviación de los valores Vs promedio obtenidos por una técnica en particular, en comparación con las otras, es similar. Respecto a la técnica Re-Mi, cabe destacar que, si bien no se ha mostrado muy precisa en este estudio, presenta un alto grado de operatividad en cuanto a implantación, ejecución y procesado de datos
Optimization of bismuth telluride films and nano-wire arrays via electrodeposition for thermoelectric applications
Comunicación presentada en el 3rd Early Stage Researchers Workshop in Nanoscience, celebrado en Madrid el 27 y 28 de junio de 2013.Due to the current world’s demand for energy, there is a great interest in thermoelectricity, which offers the
possibility of increasing the sustainability of our electrical system. Thermoelectric materials can convert heat into
electricity and vice versa, and thus they offer a way of recovering wasted heat produced in engines, industrial processes
and others into usable power. However, one of the main problems for their actual use is their low efficiency in this
conversion. This efficiency is directly related with what is called the thermoelectric figure of merit, described by
ZT=(S2·σ·T)/κ ,where S, σ, κ, and T stand for the Seebeck coefficient, electrical and thermal conductivities, and the
absolute temperature, respectively. Given that in classical physics S, σ, and κ, are correlated, the improvement of the
efficiency is not straightforward. Nevertheless, in 1993 a theoretical work suggested that the efficiency could be greatly
enhanced by reducing the dimensionality of the structures under studied and working in the nano-scale. Therefore, much
experimental effort has been done to achieve these kind of structures and in some cases, an enhancement of the ZT
value has been achieved, although this has not been due to the quantum confinement to the charge carriers, as it was
theoretically predicted, but to an increase of the κ due to the increased number of interface boundaries in nanostructures.
Among the most efficient thermoelectric materials used for applications at room temperature, bismuth telluride
(Bi2Te3) and its different alloys stand out, with a ZT for Bi2Te3of around 1 at RT [2]. We present here an optimized
method of obtaining films and nanowire arrays via electrochemical deposition in a conventional three-electrode cell.
Different ways of improving the quality of the obtained films have been studied (working electrode, constant and
pulsed potentials, different chemical baths, etc.) in order to obtain highly oriented (110) films, which are the most
favorable for out-of-plane applications. Then, nanostructuration has been achieved by changing the working
electrode to porous alumina templates and realizing the electrochemical deposition inside the pores. The samples
produced have been characterized using SEM, EDX, AFM, XRD, and Raman spectrometry, and in the case of the
films, their transport properties have also been measured.Peer Reviewe
The influence of cell size on the mechanical properties of nanocellular PMMA
Solid-state foaming experiments are conducted on three grades of polymethyl methacrylate (PMMA). Nanocellular PMMA foams are manufactured with an average cell size ranging from 20 nm to 84 nm and a relative density between 0.37 and 0.5. For benchmarking purposes, additional microcellular PMMA foams with an average cell size close to 1 µm and relative density close to that of the nanocellular foams are manufactured. Uniaxial compression tests and single edge notch bend tests are conducted on the PMMA foams. The measured Young’s modulus and yield strength of the PMMA foams are independent of cell size whereas the fracture toughness of the PMMA foam increases with decreasing average cell size from the micron range to the nanometer range.Financial assistance from MINECO, FEDER, UE (MAT2015-69234-R), the Junta of Castile and Leon (VA275P18) and Spanish Ministry of Science, Innovation and Universities (RTI2018-098749-B-I00) are gratefully acknowledged. Financial support from FPU grant FPU14/02050 (V. Bernardo) from the Spanish Ministry of Education and Junta of Castile and Leon grant (J. Martín-de León) are gratefully acknowledged. Financial support from SABIC and the EPSRC award 1611305 (F. Van Loock), and the ERC project MULTILAT (N. A. Fleck) are acknowledged too
Hybrid Monte Carlo algorithm for the double exchange model
The Hybrid Monte Carlo algorithm is adapted to the simulation of a system of classical degrees of freedom coupled to non self-interacting lattices fermions. The diagonalization of the Hamiltonian matrix is avoided by introducing a path-integral formulation of the problem, in d + 1 Euclidean space–time. A perfect action formulation allows to work on the continuum Euclidean time, without need for a Trotter–Suzuki extrapolation. To demonstrate the feasibility of the method we study the Double Exchange Model in three dimensions. The complexity of the algorithm grows only as the system volume, allowing to simulate in lattices as large as 163 on a personal computer. We conclude that the second order paramagnetic–ferromagnetic phase transition of Double Exchange Materials close to half-filling belongs to the Universality Class of the three-dimensional classical Heisenberg model
Optimization Design of RC Elevated Water Tanks under Seismic Loads
[EN] This paper deals with the seismic column design of 35 elevated RC water storage tanks. Tanks comprise a top conic trunk reservoir, a column with variable hollow square cross-sections, and a shallow foundation on a sand layer. The five-column heights considered are 20, 25, 30, 35, and 40 m. The five tanks are subjected to seven degrees of seismic loading characterized by the reference peak ground acceleration in Eurocode 8. The elevated tanks are designed against the full prescriptions of Eurocode 2, Eurocode 8, and the Spaniard Structural Code of Practice. This includes variable loads for seismicity, wind, snow, etc., together with the action of self-weight and dead loads. The optimization design method considered is a variant of the old bachelor algorithm, an adaptive threshold acceptance method with a neighborhood move based on the mutation operator from genetic algorithms. Column results show the high nonlinearity of the problem since the horizontal seismic forces depend on the rigidity and height of the columns. The main features of the optimized tanks give guidance for the practical design of this kind of elevated RC water tank.Grant PID2020-117056RB-I00 funded by MCIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe".Martínez-Martín, FJ.; Yepes, V.; Gonzalez Vidosa, F.; Hospitaler Pérez, A.; Alcalá-González, J. (2022). Optimization Design of RC Elevated Water Tanks under Seismic Loads. Applied Sciences. 12(11):1-19. https://doi.org/10.3390/app12115635119121
Linking changes in radial profiles of sap flux density with the response of water vapour exchange to water deficit
8 páginas, 5 figuras, 1 tabla, 19 referencias.-- IX International Workshop on Sap Flow, celebrado del 4-7 de junio 2013, en Gante, Bélgica.Knowledge of temporal variations in radial profiles of sap flux density (Js) and its relation to canopy water vapour exchange would help to improve our understanding of plant water relations. In this study we aimed to test if there is a consistent radial profile of Js in olive trees under optimal soil water availability and severe water stress conditions. Furthermore, if the radial profile of Js is not consistent through time we aimed to assess whether this radial variability can be explained through differential water exchange response to evaporative demand (D) of sun-exposed, new foliage and shade, old foliage. We measured sap flux density in the trunk of 6-year-old olive trees under two different irrigation treatments: a full irrigation treatment and a treatment replacing 30% of the of irrigation needs. We related the hourly radial profiles characterized with the Beta probability distribution function with independent water vapour exchange measurements at different exposures in the tree canopy (sun-exposed, young foliage and shade, old foliage). Results showed that under well irrigated conditions the shape of the radial profile of Js hardly varied, but under water deficit situations most of the sap appears to be conducted deeper into the sapwood and Js is also more variable throughout the sapwood. Accordingly, results demonstrated that in shade, old foliage water vapour exchange varied less than in sun-exposed new foliage. As a result, in days under severe water deficit, the contribution of shade old foliage to the whole tree transpiration was greater. Radial profile changes and canopy measurements were found to respond in a similar way to D. During conditions of low D and soil water deficit it was observed a greater contribution of the inner xylem to total stem flow and shade, old leaves to canopy gas exchange.Peer reviewe
Young nearby open clusters and their luminosity functions
Context. Open clusters are groups of coeval stars sharing properties such as
distance and metallicity, and they are key to understanding stellar evolution.
Aims. Our main goal is to study the evolution of open clusters with a special
focus on the universality of the luminosity function. Methods. We applied an
upgraded version of the convergent point technique on about 50 open clusters.
The selection of cluster members was based purely on the exquisite astrometry
of the Gaia DR3 and Hipparcos catalogues in the five-dimensional or full
six-dimensional space. Results. We present updated lists of bona fide members
of ~50 open clusters within 500 pc and younger than 1 Gyr, exploiting the full
depth of the third Gaia data release complemented by Hipparcos at the bright
end, excluding regions in the Galactic plane. Our catalogues also are
complemented by optical and infrared photometry from the major large-scale
public surveys. All the data will be made available on a dedicated webpage with
interactive plots and a direct link to Aladin and Vizier hosted at the Centre
de Donn\'ees de Strasbourg. We derived luminosity functions for all bound
clusters and compared them in three age groups of ~50 Myr, ~150 Myr, and ~600
Myr, discussing similarities and differences to constrain their dynamical
evolution. Conclusions. Luminosity functions of clusters at 50 Myr are more
likely similar to each other and show a greater degree of similarity than older
clusters. We explain this observation with the universal luminosity function
within the volume of our sample (500 pc). Luminosity functions of clusters with
ages similar to the Pleiades or Hyades are more diverse, perhaps due to
internal dynamical evolution, but more work is needed to provide additional
evidence.Comment: 29 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Crossed-ratchet effects and domain wall geometrical pinning
The motion of a domain wall in a two dimensional medium is studied taking
into account the internal elastic degrees of freedom of the wall and
geometrical pinning produced both by holes and sample boundaries. This study is
used to analyze the geometrical conditions needed for optimizing crossed
ratchet effects in periodic rectangular arrays of asymmetric holes, recently
observed experimentally in patterned ferromagnetic films. Geometrical
calculations and numerical simulations have been used to obtain the anisotropic
critical fields for depinning flat and kinked walls in rectangular arrays of
triangles. The aim is to show with a generic elastic model for interfaces how
to build a rectifier able to display crossed ratchet effects or effective
potential landscapes for controlling the motion of interfaces or invasion
fronts.Comment: 13 pages, 18 figure
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