2,530 research outputs found
Coupled equations for Kähler metrics and Yang-Mills connections
We study equations on a principal bundle over a compact complex manifold
coupling a connection on the bundle with a Kahler structure on the base. These
equations generalize the conditions of constant scalar curvature for a Kahler
metric and Hermite-Yang-Mills for a connection. We provide a moment map
interpretation of the equations and study obstructions for the existence of
solutions, generalizing the Futaki invariant, the Mabuchi K-energy and geodesic
stability. We finish by giving some examples of solutions.Comment: 61 pages; v2: introduction partially rewritten; minor corrections and
improvements in presentation, especially in Section 4; added references; v3:
To appear in Geom. Topol. Minor corrections and improvements, following
comments by referee
Spatial and temporal analysis of the seasonal and interannual variability in the tropical Pacific simulated with a coupled GCM
In the first part of this work, the dominant time scales that explain the tropical variability of the first SINTEX
simulation (ECHAM4(T30)-ORCA) are identified through a spectral analysis. Higher order spectral analysis is
used to examine the interactions among these time scales. The time series analyzed are an average of sea surface
temperature over the Niño3 region. The time scales obtained are compared with those identified in another coupled
GCM simulation (ECHAM4(T42)-OPYC3). The higher importance of the biannual time scale in this last is explained partly by the strength of the coupling between the annual and the biannual time scales. There is no such strong coupling in the SINTEX simulation. Important differences among the generation of the simulated warm (or cold) event suggest the need of a systematic classification to isolate their relevant features. Therefore in the second part of this work, we address this problem. A space-time cluster analysis is performed on a data set built by collecting the values of the heat content anomalies in the tropical Pacific region, in the fifteen months previous to a peak in the Niño3 Index that has been identified as a warm (or cold) event. In the case of the warm events,
three types of generation schemes are found. In two of them, there are anomalies of heat content in the west, north
and south of the equator, more than nine months before the events start. In the third case, the anomalies appear and
grow in the central equatorial Pacific. Only two types are needed to classify the generation of cold events. Negative
sea level height anomalies appear six months before the Niño3 Index reaches the (local) minimum. They are located north of the equator in one of the groups, and south of it in the other. Some of these characteristic traits also appear in observations of warm and cold events
Storage requirements for PV power ramp-rate control
Short-term variability in the power generated by large grid-connected photovoltaic (PV) plants can negatively affect power quality and the network reliability. New grid-codes require combining the PV generator with some form of energy storage technology in order to reduce short-term PV power fluctuation. This paper proposes an effective method in order to calculate, for any PV plant size and maximum allowable ramp-rate, the maximum power and the minimum energy storage requirements alike. The general validity of this method is corroborated with extensive simulation exercises performed with real 5-s one year data of 500 kW inverters at the 38.5 MW Amaraleja (Portugal) PV plant and two other PV plants located in Navarra (Spain), at a distance of more than 660 km from Amaraleja
Raman microprobe characterization of electrodeposited S-rich CuIn(S,Se)2 for photovoltaic applications: Microstructural analysis
This article reports a detailed Raman scattering and microstructural characterization of S-rich CuIn(S,Se)2 absorbers produced by electrodeposition of nanocrystalline CuInSe2 precursors and subsequent reactive annealing under sulfurizing conditions. Surface and in-depth resolved Raman microprobe measurements have been correlated with the analysis of the layers by optical and scanning electron microscopy, x-ray diffraction, and in-depth Auger electron spectroscopy. This has allowed corroboration of the high crystalline quality of the sulfurized layers. The sulfurizing conditions used also lead to the formation of a relatively thick MoS2 intermediate layer between the absorber and the Mo back contact. The analysis of the absorbers has also allowed identification of the presence of In-rich secondary phases, which are likely related to the coexistence in the electrodeposited precursors of ordered vacancy compound domains with the main chalcopyrite phase, in spite of the Cu-rich conditions used in the growth. This points out the higher complexity of the electrodeposition and sulfurization processes in relation to those based in vacuum deposition techniques
Burning in the management of heathlands of Erica ciliaris and Erica tetralix: effects on structure and diversity
Can controlled burning be used as a management tool of Erica ciliaris and Erica tetralix wet heathlands?
Two E. ciliaris and E. tetralix communities were selected and two 5 x 5 m plots were established in each.
These were then characterised on the basis of frequency and cover values and plant species composition. They
were subjected to experimental burning, after which the plots were sampled twice a year during the following
four and a half years. The results show that the cover of woody species very quickly attained the values of the
Control Plots. Diversity and species composition did not suffer notable changes during this period, however,
temporal heterogeneity indicates that the main changes occur in the first 18 months of secondary succession.
The multivariate analysis showed that the samples registered during this time were grouped as a function of
the cover values of the species, which shows that stages exist in the vegetation recovery of these communities.
The damage produced by fire in the community is minor, as a rapid recovery of the vegetation was observed, so
controlled burning is a useful tool in the management of these heathlands
Scale interactions in the tropical Atlanticvariability simulated with a coupled GCM
Warm and cold events in the Gulf of Guinea are an important feature in the interannual variability of the tropical Atlantic Ocean, and partly a manifestation of the equatorial Atlantic system's intrinsic variability. Due to the relatively reduced zonal extension of this ocean, the latter variability is comparatively weak and thus strongly modified by other factors at play, either local or remote, like the seasonal cycle or ENSO. We present here an
analysis of the tropical Atlantic variability in a 100-year-long chunk of the output of a coupled GCM. Through it,
we obtain a better understanding of this variability and of its interactions with the seasonal cycle and with the ENSO signal. Following hints in the observations, we separate warm or cold events of the simulation in a few
types, according to their similarities and differences. This classification is carried out as a spatio-temporal cluster analysis of the values, from nine months before up to the peak of the event, of the heat content anomalies. This is an optimal variable to monitor the generation of the events. One of the warm event classes can be explained by ENSO interactions. One of the cold event types can be explained by this influence as well, while the seasonal
interactions might explain the characteristics of another of them
Spatial and temporal analysis of the seasonal and interannual variability in the tropical Pacific simulated with a coupled GCM
In the first part of this work, the dominant time scales that explain the tropical variability of the first SINTEX
simulation (ECHAM4(T30)-ORCA) are identified through a spectral analysis. Higher order spectral analysis is
used to examine the interactions among these time scales. The time series analyzed are an average of sea surface
temperature over the Niño3 region. The time scales obtained are compared with those identified in another coupled
GCM simulation (ECHAM4(T42)-OPYC3). The higher importance of the biannual time scale in this last is explained partly by the strength of the coupling between the annual and the biannual time scales. There is no such strong coupling in the SINTEX simulation. Important differences among the generation of the simulated warm (or cold) event suggest the need of a systematic classification to isolate their relevant features. Therefore in the second part of this work, we address this problem. A space-time cluster analysis is performed on a data set built by collecting the values of the heat content anomalies in the tropical Pacific region, in the fifteen months previous to a peak in the Niño3 Index that has been identified as a warm (or cold) event. In the case of the warm events,
three types of generation schemes are found. In two of them, there are anomalies of heat content in the west, north
and south of the equator, more than nine months before the events start. In the third case, the anomalies appear and
grow in the central equatorial Pacific. Only two types are needed to classify the generation of cold events. Negative
sea level height anomalies appear six months before the Niño3 Index reaches the (local) minimum. They are located north of the equator in one of the groups, and south of it in the other. Some of these characteristic traits also appear in observations of warm and cold events
Non-Abelian Vortices, Super-Yang-Mills Theory and Spin(7)-Instantons
We consider a complex vector bundle E endowed with a connection A over the
eight-dimensional manifold R^2 x G/H, where G/H = SU(3)/U(1)xU(1) is a
homogeneous space provided with a never integrable almost complex structure and
a family of SU(3)-structures. We establish an equivalence between G-invariant
solutions A of the Spin(7)-instanton equations on R^2 x G/H and general
solutions of non-Abelian coupled vortex equations on R^2. These vortices are
BPS solitons in a d=4 gauge theory obtained from N=1 supersymmetric Yang-Mills
theory in ten dimensions compactified on the coset space G/H with an
SU(3)-structure. The novelty of the obtained vortex equations lies in the fact
that Higgs fields, defining morphisms of vector bundles over R^2, are not
holomorphic in the generic case. Finally, we introduce BPS vortex equations in
N=4 super Yang-Mills theory and show that they have the same feature.Comment: 14 pages; v2: typos fixed, published versio
Calibración de Microscopios Confocales
El microscopio confocal ha sido durante mucho tiempo un instrumento de observación tridimensional con múltiples aplicaciones especialmente dentro de la biología. Sin embargo en los últimos años ha comenzado a ser utilizado como instrumento de medida en diferentes áreas de la ingeniería. En la actualidad existen muchas especificaciones de productos (dimensionales, angulares, acabado superficial) en las escalas micrométricas y nanométricas que pueden o podrían ser verificadas utilizando este instrumento. Pero para que esta verificación sea válida dentro de un sistema de calidad el microscopio confocal debe ser trazable. Esta ponencia presenta una solución sencilla a este problema implementada en el Centro Láser de la Universidad Politécnica de Madrid (UPM) que ha permitido dotar de trazabilidad a las medidas dimensionales realizadas en el plano XY y en el eje Z de su microscopio confocal.
The confocal microscope has been a three-dimensional observation instrument with multiple applications especially in biology. However in recent years has begun to be used as a measuring instrument contact in various engineering fields. At present there are many product specifications (size, angular, surface roughness) in the micrometer and nano scales that can or could be verified using this instrument. But this verification is only valid within a quality system if the confocal microscope is traceable. This paper presents a simple solution to this problem implemented in the Laser Centre of the Polytechnic University of Madrid (UPM). This solution provides traceablity to the size measurements made in the XY plane and the Z-axis
Leaders' sustainability competences and small and medium‐sized enterprises outcomes: the role of social entrepreneurial orientation
Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGThe market for socially conscious products and services has grown exponentially in the last years. Consequently, adding social value is among the great challenges that companies have to face nowadays. In view of this, companies need leaders with a set of specific skills that prepares them to act and compete in this new environment. This is especially true for small and medium-sized enterprises (SMEs), which are even more dependent on their leaders' competences. The aim of this article is to analyse the influence of leaders' sustainability competences on the social entrepreneurial orientation of SMEs of the tourism sector, as well as the influence of this strategy on the firm's performance. The methodology used to validate the measurement scales is exploratory and confirmatory factor analysis and the structural equation modelling technique is applied to analyse the causal relationships proposed in the model. The results show that sustainability competences positively affect social entrepreneurial orientation; specifically, the social risk-taking and proactivity competence has a positive influence on the economic and social performance of SMEs, and in particular, on their green innovation performance. These results highlight the key role that leaders' competences have in SMEs' social orientation and thus, the importance of training in competences for sustainable development
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