4,980 research outputs found
One-loop renormalization of the electroweak chiral Lagrangian with a light Higgs
We consider the general chiral effective action which parametrizes the
nonlinear realization of the spontaneous breaking of the electroweak symmetry
with a light Higgs, and compute the one-loop ultraviolet divergences coming
from Higgs and electroweak Goldstone fluctuations using the background field
method. The renormalization of the divergences is carried out through operators
of next-to-leading order in the chiral counting, i.e. of O(p^4). Being of the
same order in power counting, the logarithmic corrections linked to these
divergences can be as important as the tree-level contributions from the O(p^4)
operators, and must be accounted for in the phenomenological analysis of
experimental data. Deviations in the O(p^2) (leading-order) couplings with
respect to the Standard Model values, e.g., in the h->WW coupling, would
generate contributions from the 1-loop chiral logarithms computed in this work
to a vast variety of observables, which do not have a counterpart in the
conventional electroweak effective theory with a linearly transforming Higgs
complex doublet.Comment: 6 page
Assessment of the vegetation cover in a burned area 22-years ago using remote sensing techniques and GIS analysis (Sierra de las Nieves, South of Spain).
The study aim was to characterize the vegetation cover in a burned area 22-years ago considering the previous
situation to wildfire in 1991 and the current one in 2013. The objectives were to: (i) compare the current and previous
vegetation cover to widlfire; (ii) evaluate whether the current vegetation has recovered the previous cover to
wildfire; and (iii) determine the spatial variability of vegetation recovery after 22-years since the wildfire.
The study area is located in Sierra de las Nieves, South of Spain. It corresponds to an area affected by a wildfire in
August 8th, 1991. The burned area was equal to 8156 ha. The burn severity was spatially very high. The main geographic
features of the burned area are: mountainous topography (altitudes ranging from 250 m to 1500 m; slope
gradient >25Remote sensing techniques and GIS analysis has been applied to achieve the objectives. Landsat 5 and
Landsat 8 images were used: July 13th, 1991 and July 1st, 2013, for the previous wildfire situation and 22-years
after, respectively. The 1990 CORINE land cover was also considered to map 1991 land uses prior the wildfire.
Likewise, the Andalucía Regional Government wildfire historic records were used to select the burned area and
its geographical limit. 1991 and 2013 land cover map were obtained by means of object-oriented classifications.
Also, NDVI and PVI1 vegetation indexes were calculated and mapped for both years. Finally, some images transformations
and kernel density images were applied to determine the most recovered areas and to map the spatial
concentration of bare soil and pine cover areas in 1991 and 2013, respectively.
According to the results, the combination of remote sensing and GIS analysis let map the most recovered areas
affected by the wildfire in 1991. The vegetation indexes indicated that the vegetation cover in 2013 was still lower
than that mapped just before the 1991 widlfire in most of the burned area after 22-years. This result was also confirmed
by other techniques applied. Finally, the kernel density surface let identify and locate the most recovered
areas of pine cover as well as those areas that still remain totally or partially uncovered (bare soil.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Analysis of heavy rainfall in two contrasted Mediterranean watersheds from 1993 to 2017
"Despite the proximity of the watersheds there are strong"
"environmental contrasts between both."
"• The current rainfall dynamics follows a trend towards concentration in fewer days."
"• A rainfall cataloged as torrential by the AEMET (≥ 100 / 24h, ≥60 mmh-1) is not necessary to activate erosion and degradation processes, especially when the system conditions are vulnerable. There are downpours hidden in the hourly precipitation data that get at very high intensities."
"• It is considered the need to analyze exhaustively the characteristics of a given system, in order to establish what capacity of response has a specific area in an event of extreme precipitation.
The geomorphological rainfall in the Mediterranean landscape modeling
The kinetic energy derived from the heavy rainfall constitutes one of the main factors of the geomorphological
processes in Mediterranean environments, as well as in the landscape and the ecosystem modeling, resulting from
its extraordinary spatial and temporal variability.
When the rainfall is analyzed, particularly in Mediterranean climate and in the context of Climate Change, it is
not only necessary to consider the total rainfall collected annually, but also it is essential to take into account other
variables as intensity, duration, and frequency.
A series of extreme rainfall databases have been analyzed for the last 25 years (1993-2017), with daily, horary
and 10-minutes registers. These have been obtained from different weather stations belonging to the Agencia
Estatal de Meteorología –AEMET- and the S.A.I.H. Hydrosur Network, spatially distributed in two regions of the
province of Malaga. (Guadalhorce and Axarquía). The results show the limited frequency of the events considered
as torrential rainfall according to the Agencia Estatal de Meteorología criteria ( 100mm/24h; 60mm/60’) and
a high occurrence of shorts heavy downpours ( 10mm/10’), especially in recent years. These downpours have
been classified as “geomorphological rainfall”, short events capable of activating hydro-soil processes, owing to
its high intensity and the vulnerable conditions of the eco-geomorphological system in the study areas
Available water modifications by topsoil treatments under mediterranean semiarid conditions: afforestation plan
During dry periods in the Mediterranean area, the lack of water entering the soil matrix reduces organic contribu-
tions to the soil. These processes lead to reduced soil fertility and soil vegetation recovery which creates a positive
feedback process that can lead to desertification. Restoration of native vegetation is the most effective way to
regenerate soil health, and control runoff and sediment yield.
In Mediterranean areas, after a forestry proposal, it is highly common to register a significant number of
losses for the saplings that have been introduced due to the lack of rainfall. When no vegetation is established,
organic amendments can be used to rapidly protect the soil surface against the erosive forces of rain and runoff.
In this study we investigated the hydrological effects of five soil treatments in relation to the temporal vari-
ability of the available water for plants. Five amendments were applied in an experimental set of plots: straw
mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent
polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and
amendments were mixed with the soil at the rate 10 Mg ha-1.
In control plots, during June, July, August and September, soils were registered below the wilting point,
and therefore, in the area of water unusable by plants. These months were coinciding with the summer mediter-
ranean drought. This fact justifies the high mortality found on plants after the seeding plan. Similarly, soils have
never exceeded the field capacity value measured for control plots. Conversely, in the straw and pinus mulch, soils
were above the wilting point during a longer time than in control plots. Thus, the soil moisture only has stayed
below the 4.2 pF suction in July, July and August. Regarding the amount of water available was also higher,
especially in the months of December, January and February. However, the field capacity value measured has not
showed any differences regarding the control. For these treatments, the survival sapling rates measured were the
highest.
Sludge, manure and polymers showed a moisture retention capacity slightly more limited than straw and
pinus mulch. Likewise, it has been found that the area of usable water by plants was also lower, especially during
the months of January and February. This situation is especially sharpened in plots amended with manure. In
this treatment, the upper part of the soil profile was below the wilting point for six months a year (from April to
August). For this treatment, the survival sapling rates measured were the lowest.
In conclusion, from a land management standpoint, the pinus and straw mulch treatments have been shown
as effective methods reducing water stress for plants. In this research, mulching has been proved as a significant
method to reduce the mortality sapling rates during the mediterranean summer drought.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
An experimental and modelling exploration of the host-sanction hypothesis in legume-rhizobia mutualism
Despite the importance of mutualism as a key ecological process, its persistence in nature is difficult to explain since the existence of exploitative, 'cheating' partners that could erode the interaction is common. By analogy with the proposed policing strategy stabilizing intraspecific cooperation, host sanctions against non N2 fixing, cheating symbionts have been proposed as a force stabilizing mutualism in legume-Rhizobium symbiosis. Following this proposal, penalizations would include decreased nodular rhizobial viability and/or early nodule senescence in nodules occupied by cheating rhizobia. In this work, we analyze the stability of Rhizobium-legume symbiosis when "cheating" strains are present, using an experimental and modelling approach. We used split-root experiments with soybean plants inoculated with two rhizobial strains, a cooperative, normal N2 fixing strain and an isogenic non-fixing, “perfect” cheating mutant derivative that lacks nitrogenase activity but has the same nodulation abilities inoculated to split-root plants. We found no experimental evidence of functioning plant host sanctions to cheater rhizobia based on nodular rhizobia viability and nodule senescence and maturity molecular markers. Based on these experiments, we developed a population dynamic model with and without the inclusion of plant host sanctions. We show that plant populations persist in spite of the presence of cheating rhizobia without the need of incorporating any sanction against the cheater populations in the model, under the realistic assumption that plants can at least get some amount of fixed N2 from the effectively mutualistic rhizobia occupying some nodules. Inclusion of plant sanctions merely reduces the time needed for reaching plant population equilibrium and leads to the unrealistic effect of ultimate extinction of cheater strains in soil. Our simulation results are in agreement with increasing experimental evidence and theoretical work showing that mutualisms can persist or even improve in presence of cheating partners
Impact of prescribed fire in soil properties after 5-years: experimental study.
Wildfires are a serious problem in areas with a Mediterranean climate owing to the hot summers and drought conditions providing perfect conditions for wildfire, especially when there are large amounts of fuel accumulation and continuity between forested areas. In the Mediterranean, high severity fires that spread rapidly are common and difficult to be extinguished. Thus, the identification of tools to reduce fire spread and minimize their incidence and effects is crucial. Preventive forestry is a good tool for achieving forest structures with lower amounts of fuel and a greater resistance to fire. Prescribed fire is the planned use of fire under predetermined weather, fuel and topographic parameters to achieve clearly defined objectives as controlling fire regimes by managing fuel, counteracting the disappearance of biomass-consuming land management practices and reducing the overall fire risk. Normally, prescribed fires are low intensity fires and, if managed adequately, do not cause any damage to trees, especially in Mediterranean ecosystems where trees are resilient to fire. Besides, prescribed fires usually have different impacts on soils, water resources, biodiversity, the risk-reduction of wildfires and carbon storage. Prescribed fires usually are of low/moderate severity. Because of this, the effects of prescribed fires on soils properties may vary from one site to another. The objectives of our study are to: i) determine the impact of the prescribed fire just after and ii) 5-years later with respect to natural conditions. To do this, in 2011, a prescribed fire was conducted in one experimental area of Mediterranean rangeland. After the fire, soil samples (0-5 cm of depth) were taken in burned and unburned plots in order to analyse: pH, electrical conductivity (EC), soil organic carbon, cationic exchangeable capacity (CEC), aggregate stability (AS), and hydrophobicity. The results indicated that: i) prescribed fire only had significantly effects in CEC just after the fire; 5-years after, there were no significant differences between the unburned and burned plots, but two soil properties significantly changed when burned soil samples from 2016 and 2011 were compared: EC and AS in the fraction of 0.053-0.125 mm. In general, the soil properties were not substantially modified by the prescribed fire, supporting the idea it is a very useful tool with very low impact for managing Mediterranean rangelands in order to reduce fuel accumulation and fire risk.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Integrability of Stochastic Birth-Death processes via Differential Galois Theory
Stochastic birth-death processes are described as continuous-time Markov
processes in models of population dynamics. A system of infinite, coupled
ordinary differential equations (the so-called master equation) describes the
time-dependence of the probability of each system state. Using a generating
function, the master equation can be transformed into a partial differential
equation. In this contribution we analyze the integrability of two types of
stochastic birth-death processes (with polynomial birth and death rates) using
standard differential Galois theory. We discuss the integrability of the PDE
via a Laplace transform acting over the temporal variable. We show that the PDE
is not integrable except for the (trivial) case in which rates are linear
functions of the number of individuals
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