355 research outputs found
Anthocyanins are Key Regulators of Drought Stress Tolerance in Tobacco
Abiotic stresses will be one of the major challenges for worldwide food supply in the near future. Therefore, it is important to understand the physiological mechanisms that mediate plant responses to abiotic stresses. When subjected to UV, salinity or drought stress, plants accumulate specialized metabolites that are often correlated with their ability to cope with the stress. Among them, anthocyanins are the most studied intermediates of the phenylpropanoid pathway. However, their role in plant response to abiotic stresses is still under discussion. To better understand the effects of anthocyanins on plant physiology and morphogenesis, and their implications on drought stress tolerance, we used transgenic tobacco plants (AN1), which over-accumulated anthocyanins in all tissues. AN1 plants showed an altered phenotype in terms of leaf gas exchanges, leaf morphology, anatomy and metabolic profile, which conferred them with a higher drought tolerance compared to the wild-type plants. These results provide important insights for understanding the functional reason for anthocyanin accumulation in plants under stress
Landscape statistics of the p-spin Ising model
The statistical properties of the local optima (metastable states) of the
infinite range Ising spin glass with p-spin interactions in the presence of an
external magnetic field h are investigated analytically. The average number of
optima as well as the typical overlap between pairs of identical optima are
calculated for general p. Similarly to the thermodynamic order parameter, for
p>2 and small h the typical overlap q_t is a discontinuous function of the
energy. The size of the jump in q_t increases with p and decreases with h,
vanishing at finite values of the magnetic field.Comment: 12 pages,te
Modeling Watershed Response in Semiarid Regions With High-Resolution Synthetic Aperture Radars
In this paper, we propose a methodology devoted to exploit the outstanding characteristics of COSMO-SkyMed for monitoring water bodies in semiarid countries at a scale never experienced before. The proposed approach, based on appropriate registration, calibration, and processing of synthetic aperture radar (SAR) data, allows outperforming the previously available methods for monitoring small reservoirs, mainly carried out with optical data, and severely limited by the presence of cloud coverage, which is a frequent condition in wet season. A tool has been developed for computing the water volumes retained in small reservoirs based on SAR-derived digital elevation model. These data have been used to derive a relationship between storage volumes and surface areas that can be used when bathymetric information is unavailable. Due to the lack of direct measures of river's discharge, the time evolution of water volumes retained at reservoirs has been used to validate a simple rainfall-runoff hydrological model that can provide useful recommendation for the management of small reservoirs. Operational scenarios concerning the improvement in the efficiency of reservoirs management and the estimation of their impact on downstream area point out the applicative outcomes of the proposed method
Fractal geometry of spin-glass models
Stability and diversity are two key properties that living entities share
with spin glasses, where they are manifested through the breaking of the phase
space into many valleys or local minima connected by saddle points. The
topology of the phase space can be conveniently condensed into a tree
structure, akin to the biological phylogenetic trees, whose tips are the local
minima and internal nodes are the lowest-energy saddles connecting those
minima. For the infinite-range Ising spin glass with p-spin interactions, we
show that the average size-frequency distribution of saddles obeys a power law
, where w=w(s) is the number of minima that can be
connected through saddle s, and D is the fractal dimension of the phase space
Fractal to Nonfractal Phase Transition in the Dielectric Breakdown Model
A fast method is presented for simulating the dielectric-breakdown model
using iterated conformal mappings. Numerical results for the dimension and for
corrections to scaling are in good agreement with the recent RG prediction of
an upper critical , at which a transition occurs between branching
fractal clusters and one-dimensional nonfractal clusters.Comment: 5 pages, 7 figures; corrections to scaling include
Characteristic distributions of finite-time Lyapunov exponents
We study the probability densities of finite-time or \local Lyapunov
exponents (LLEs) in low-dimensional chaotic systems. While the multifractal
formalism describes how these densities behave in the asymptotic or long-time
limit, there are significant finite-size corrections which are coordinate
dependent. Depending on the nature of the dynamical state, the distribution of
local Lyapunov exponents has a characteristic shape. For intermittent dynamics,
and at crises, dynamical correlations lead to distributions with stretched
exponential tails, while for fully-developed chaos the probability density has
a cusp. Exact results are presented for the logistic map, . At
intermittency the density is markedly asymmetric, while for `typical' chaos, it
is known that the central limit theorem obtains and a Gaussian density results.
Local analysis provides information on the variation of predictability on
dynamical attractors. These densities, which are used to characterize the {\sl
nonuniform} spatial organization on chaotic attractors are robust to noise and
can therefore be measured from experimental data.Comment: To be appear in Phys. Rev
Rupture by damage accumulation in rocks
The deformation of rocks is associated with microcracks nucleation and
propagation, i.e. damage. The accumulation of damage and its spatial
localization lead to the creation of a macroscale discontinuity, so-called
"fault" in geological terms, and to the failure of the material, i.e. a
dramatic decrease of the mechanical properties as strength and modulus. The
damage process can be studied both statically by direct observation of thin
sections and dynamically by recording acoustic waves emitted by crack
propagation (acoustic emission). Here we first review such observations
concerning geological objects over scales ranging from the laboratory sample
scale (dm) to seismically active faults (km), including cliffs and rock masses
(Dm, hm). These observations reveal complex patterns in both space (fractal
properties of damage structures as roughness and gouge), time (clustering,
particular trends when the failure approaches) and energy domains (power-law
distributions of energy release bursts). We use a numerical model based on
progressive damage within an elastic interaction framework which allows us to
simulate these observations. This study shows that the failure in rocks can be
the result of damage accumulation
Curvature fluctuations and Lyapunov exponent at Melting
We calculate the maximal Lyapunov exponent in constant-energy molecular
dynamics simulations at the melting transition for finite clusters of 6 to 13
particles (model rare-gas and metallic systems) as well as for bulk rare-gas
solid. For clusters, the Lyapunov exponent generally varies linearly with the
total energy, but the slope changes sharply at the melting transition. In the
bulk system, melting corresponds to a jump in the Lyapunov exponent, and this
corresponds to a singularity in the variance of the curvature of the potential
energy surface. In these systems there are two mechanisms of chaos -- local
instability and parametric instability. We calculate the contribution of the
parametric instability towards the chaoticity of these systems using a recently
proposed formalism. The contribution of parametric instability is a continuous
function of energy in small clusters but not in the bulk where the melting
corresponds to a decrease in this quantity. This implies that the melting in
small clusters does not lead to enhanced local instability.Comment: Revtex with 7 PS figures. To appear in Phys Rev
Aszites, Pfortaderthrombose und hepatische Enzephalopathie bei Leberzirrhose: Aktuelle Therapieempfehlungen
Treatment of Ascites, Portal Vein Thrombosis and Hepatic Encephalopathy in Patients with Cirrhosis of the Liver Background: Ascites, portal vein thrombosis and hepatic encephalopathy are important complications of cirrhosis of the liver. Guidelines for the treatment of ascites have recently been published. Method: This manuscript summarizes up-to-date recommendations on the basis of the DGVS S3 guideline and of other guidelines as well as of the authors' experience. Results and Conclusions: TIPS (transjugular intrahepatic porto-systemic shunt) is the preferred treatment for refractory or recidivant ascites unless there are contraindications. The therapy of hepatorenal syndrome type 1 with albumin and the vasoconstrictor Terlipressin has been proven effective. Treatment of portal vein thrombosis comprises a strategy of anticoagulation, TIPS and liver transplantation. The most important therapeutic strategy for hepatic encephalopathy is the search for as well as the treatment of trigger events. Rifaximin is being increasingly used for the treatment and prophylaxis of hepatic encephalopathy
Dragon-kings: mechanisms, statistical methods and empirical evidence
This introductory article presents the special Discussion and Debate volume
"From black swans to dragon-kings, is there life beyond power laws?" published
in Eur. Phys. J. Special Topics in May 2012. We summarize and put in
perspective the contributions into three main themes: (i) mechanisms for
dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii)
empirical evidence in a large variety of natural and social systems. Overall,
we are pleased to witness significant advances both in the introduction and
clarification of underlying mechanisms and in the development of novel
efficient tests that demonstrate clear evidence for the presence of
dragon-kings in many systems. However, this positive view should be balanced by
the fact that this remains a very delicate and difficult field, if only due to
the scarcity of data as well as the extraordinary important implications with
respect to hazard assessment, risk control and predictability.Comment: 20 page
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