481 research outputs found
One-loop effective potential in M4 x T2 with and without 't Hooft flux
We review the basic notions of compactification in the presence of a
background flux. In extra-dimentional models with more than five dimensions,
Scherk and Schwarz boundary conditions have to satisfy 't Hooft consistency
conditions. Different vacuum configurations can be obtained, depending whether
trivial or non-trivial 't Hooft flux is considered. The presence of the
"magnetic" background flux provide, in addition, a mechanism for producing
four-dimensional chiral fermions. Particularizing to the six-dimensional case,
we calculate the one-loop effective potential for a U(N) gauge theory on M4 x
T2. We firstly review the well known results of the trivial 't Hooft flux case,
where one-loop contributions produce the usual Hosotani dynamical symmetry
breaking. Finally we applied our result for describing, for the first time, the
one-loop contributions in the non-trivial 't Hooft flux case
Elucidating the photosynthetic responses in chlorophyll-deficient soybean (Glycine max, L.) leaf
Chlorophyll (Chl)-deficient plants can potentially increase global surface albedo of mono-cropping systems, and simultaneously maintain a similar photosynthetic efficiency by increasing light canopy penetration and thus lowering investment in pigments. However, some previous studies have shown that pale mutants might reduce productivity in field conditions. Such lower yields were suspected to be due to loss of photosynthetic efficiency at leaf level during light fluctuations as a consequence of reduced capacity and slower relaxation of non-photochemical quenching (NPQ) of Chl fluorescence. In this paper, we tested this hypothesis by comparing, CO2 assimilation (A), photosystem II (PSII) efficiency (ΦPSII), photochemical quenching and NPQ, electron transport rate (ETR) and fluorescence yield (Fyield) in a green soybean (Glycine max L.) cultivar (Eiko) and in a Chl-deficient (MinnGold) mutant under dynamically fluctuating light conditions. MinnGold had significantly slower induction of ETR and lower A and ETR than Eiko, but there was little difference in ΦPSII between the two genotypes, suggesting that the lower photosynthesis of MinnGold was mainly due to lower light energy absorption by a Chl-deficient leaf. The NPQ capacity was also smaller in MinnGold than in Eiko. As for the kinetics of the rapidly inducible component of NPQ, MinnGold showed slower induction, not relaxation, than Eiko. The combination of the effect of Chl-deficiency on lower photosynthesis, NPQ capacity and slower NPQ induction may explain the lower biomass accumulation of MinnGold in the field. Our physiological observations, combined with fluorescence kinetics, can serve as a basis to parameterize Chl content in modelling radiative transfer and photosynthesis for upscaling measures of plant and ecosystem productivity by a big leaf model
Symmetry breaking from Scherk-Schwarz compactification
We analyze the classical stable configurations of an extra-dimensional gauge
theory, in which the extra dimensions are compactified on a torus. Depending on
the particular choice of gauge group and the number of extra dimensions, the
classical vacua compatible with four-dimensional Poincar\'e invariance and zero
instanton number may have zero energy. For SU(N) on a two-dimensional torus, we
find and catalogue all possible degenerate zero-energy stable configurations in
terms of continuous or discrete parameters, for the case of trivial or
non-trivial 't Hooft non-abelian flux, respectively. We then describe the
residual symmetries of each vacua.Comment: 24 pages, 1 figure, Section 4 modifie
Minimal gauge-Higgs unification with a flavour symmetry
We show that a flavour symmetry a la Froggatt-Nielsen can be naturally
incorporated in models with gauge-Higgs unification, by exploiting the heavy
fermions that are anyhow needed to realize realistic Yukawa couplings. The case
of the minimal five-dimensional model, in which the SU(2)_L x U(1)_Y
electroweak group is enlarged to an SU(3)_W group, and then broken to U(1)_em
by the combination of an orbifold projection and a Scherk-Schwarz twist, is
studied in detail. We show that the minimal way of incorporating a U(1)_F
flavour symmetry is to enlarge it to an SU(2)_F group, which is then completely
broken by the same orbifold projection and Scherk-Schwarz twist. The general
features of this construction, where ordinary fermions live on the branes
defined by the orbifold fixed-points and messenger fermions live in the bulk,
are compared to those of ordinary four-dimensional flavour models, and some
explicit examples are constructed.Comment: LaTex, 37 pages, 2 figures; some clarifying comments and a few
references adde
Brain-Inspired Computational Intelligence via Predictive Coding
Artificial intelligence (AI) is rapidly becoming one of the key technologies
of this century. The majority of results in AI thus far have been achieved
using deep neural networks trained with the error backpropagation learning
algorithm. However, the ubiquitous adoption of this approach has highlighted
some important limitations such as substantial computational cost, difficulty
in quantifying uncertainty, lack of robustness, unreliability, and biological
implausibility. It is possible that addressing these limitations may require
schemes that are inspired and guided by neuroscience theories. One such theory,
called predictive coding (PC), has shown promising performance in machine
intelligence tasks, exhibiting exciting properties that make it potentially
valuable for the machine learning community: PC can model information
processing in different brain areas, can be used in cognitive control and
robotics, and has a solid mathematical grounding in variational inference,
offering a powerful inversion scheme for a specific class of continuous-state
generative models. With the hope of foregrounding research in this direction,
we survey the literature that has contributed to this perspective, highlighting
the many ways that PC might play a role in the future of machine learning and
computational intelligence at large.Comment: 37 Pages, 9 Figure
Interventional treatment options for management of delayed arterial hemorrhage after major hepato-pancreatic-biliary surgery.
Mapping litter decomposition by remote-detected indicators
Leaf litter decomposition is a key process for the functioning of natural ecosystems. An important limiting factor
for this process is detritus availability, which we have estimated by remote sensed indices of canopy green
biomass (NDVI). Here, we describe the use of multivariate geostatistical analysis to couple in situ measures with
hyper-spectral and multi-spectral remote-sensed data for producing maps of litter decomposition. A direct relationship
between the decomposition rates in four different CORINE habitats and NDVI, calculated at different
scales from Landsat ETM+ multi-spectral data and MIVIS hyper-spectral data was found. Variogram analysis
was used to evaluate the spatial properties of each single variable and their common interaction. Co-variogram
and co-kriging analysis of the two variables turned out to be an effective approach for decomposition mapping
from remote-sensed spatial explicit data
Mapping and assessment of ecosystems and their services. Urban ecosystems
Action 5 of the EU Biodiversity Strategy to 2020 requires member states to Map and Assess the state of Ecosystems and their Services (MAES). This report provides guidance for mapping and assessment
of urban ecosystems. The MAES urban pilot is a collaboration between the European Commission, the European Environment Agency, volunteering Member States and cities, and stakeholders. Its ultimate
goal is to deliver a knowledge base for policy and management of urban ecosystems by analysing urban green infrastructure, condition of urban ecosystems and ecosystem services. This report presents guidance for mapping urban ecosystems and includes an indicator framework to assess the condition of urban ecosystems and urban ecosystem services. The scientific framework of mapping and assessment is designed to support in particular urban planning policy and policy on green infrastructure at urban, metropolitan and regional scales. The results are based on the following different sources of information: a literature survey of 54 scientific articles, an online-survey (on urban ecosystems, related policies and planning instruments and with participation of 42 cities), ten case studies (Portugal: Cascais, Oeiras, Lisbon; Italy: Padua, Trento, Rome; The Netherlands: Utrecht; Poland: Poznań; Spain: Barcelona; Norway: Oslo), and a two-day expert workshop. The case studies constituted the core of the MAES urban pilot. They provided real examples and applications of how mapping and assessment can be organized to support policy; on top, they provided the necessary expertise to select a set of final indicators for condition and ecosystem services. Urban ecosystems or cities are defined here as socio-ecological systems which are composed of green infrastructure and built infrastructure. Urban green infrastructure (GI) is understood in this report as the multi-functional network of urban green spaces situated within the boundary of the urban ecosystem. Urban green spaces are the structural components of urban GI.
This study has shown that there is a large scope for urban ecosystem assessments. Firstly, urban policies increasingly use urban green infrastructure and nature-based solutions in their planning process. Secondly, an increasing amount of data at multiple spatial scales is becoming available to support these policies, to provide a baseline, and to compare or benchmark cities with respect to the extent and management of the urban ecosystem. Concrete examples are given on how to delineate urban ecosystems, how to choose an appropriate spatial scale, and how to map urban ecosystems based on a combination of national or European datasets (including Urban Atlas) and locally collected information (e.g., location of trees). Also examples of typologies for urban green spaces are presented.
This report presents an indicator framework which is composed of indicators to assess for urban ecosystem condition and for urban ecosystem services. These are the result of a rigorous selection
process and ensure consistent mapping and assessment across Europe. The MAES urban pilot will continue with work on the interface between research and policy. The framework presented in this report needs to be tested and validated across Europe, e.g. on its applicability at city scale, on how far the methodology for measuring ecosystem condition and ecosystem service delivery in urban areas can be used to assess urban green infrastructure and nature-based solutions
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