Loschmidt echo for local perturbations: non-monotonous cross-over from the Fermi-golden-rule to the escape-rate regime

We address the sensitivity of quantum mechanical time evolution by considering the time decay of the Loschmidt echo (LE) (or fidelity) for local perturbations of the Hamiltonian. Within a semiclassical approach we derive analytical expressions for the LE decay for chaotic systems for the whole range from weak to strong local perturbations and identify different decay regimes which complement those known for the case of global perturbations. For weak perturbations a Fermi-golden-rule (FGR) type behavior is recovered. For strong perturbations the escape-rate regime is reached, where the LE decays exponentially with a rate independent of the perturbation strength. The transition between the FGR regime and the escape-rate regime is non-monotonic, i.e. the rate of the exponential time-decay of the LE oscillates as a function of the perturbation strength. We further perform extensive quantum mechanical calculations of the LE based on numerical wave packet evolution which strongly support our semiclassical theory. Finally, we discuss in some detail possible experimental realizations for observing the predicted behavior of the LE.Comment: 27 pages, 7 figures; important changes throughout the pape

Secretory structures in plants: lessons from the Plumbaginaceae on their origin, evolution and roles in stress tolerance

Special IssueThe Plumbaginaceae (non-core Caryophyllales) is a family well known for species adapted to a wide range of arid and saline habitats. Of its salt-tolerant species, at least 45 are in the genus Limonium; two in each of Aegialitis, Limoniastrum and Myriolimon, and one each in Psylliostachys, Armeria, Ceratostigma, Goniolimon and Plumbago. All the halophytic members of the family have salt glands, which are also common in the closely related Tamaricaceae and Frankeniaceae. The halophytic species of the three families can secrete a range of ions (Na+, K+, Ca2+, Mg2+, Cl−, HCO3 −, SO4 2-) and other elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn). Salt glands are, however, absent in salt-tolerant members of the sister family Polygonaceae. We describe the structure of the salt glands in the three families and consider whether glands might have arisen as a means to avoid the toxicity of Na+ and/or Cl− or to regulate Ca2+ concentrations within the leaves. We conclude that the establishment of lineages with salt glands took place after the split between the Polygonaceae and its sister group the Plumbaginaceaeinfo:eu-repo/semantics/publishedVersio

An evaluation of a general circulation model (GCM) and the NCEP-NCAR reanalysis data for winter precipitation in Greece

In this study, an attempt is made to evaluate winter precipitation data derived from the general circulation model (GCM) - HadAM3P (atmospherical circulation model - Hadley Center) and from the National Center for Environmental Prediction-National Center of Atmospheric Research (NCEP-NCAR) reanalysis project for the period 1960-1990. These data sets are compared on a seasonal basis (winter) with observational data derived from stations over Greece. More specifically, the suitability of their average distributions and their spatial and temporal variability is examined. The methods used are principal component analysis (PCA) and canonical correlation analysis (CCA). The connection between the precipitation data sets and five cyclonic circulation types, from a daily catalogue, is also studied. With respect to the spatial distribution of the mean precipitation amounts, NCEP data show better agreement with the observational data compared to the modeled data. However, both NCEP and HadAM3P values are generally underestimated. Moreover, it seems that the HadAM3P is able to capture and reproduce quite satisfactorily the relationship between the precipitation data and the circulation types, but inadequately simulates the impact of orography and the Aegean Sea. Finally, the links between the precipitation variability in Greece and the European 500 hPa variability given by CCA seem to be fairly well reproduced by the model. Copyright © 2006 Royal Meteorological Society

Simulation of seasonal precipitation and raindays over Greece: A statistical downscaling technique based on artificial neural networks (ANNs)

A statistical downscaling technique based on artificial neural network (ANN) was employed for the estimation of local changes on seasonal (winter, spring) precipitation and raindays for selected stations over Greece. Empirical transfer functions were derived between large-scale predictors from the NCEP/NCAR reanalysis and local rainfall parameters. Two sets of predictors were used: (1) the circulation-based 500 hPa and (2) its combination along with surface specific humidity and raw precipitation data (nonconventional predictor). The simulated time series were evaluated against observational data and the downscaling model was found efficient in generating winter and spring precipitation and raindays. The temporal evolution of the estimated variables was well captured, for both seasons. Generally, the use of the nonconventional predictors are attributed to the improvement of the simulated results. Subsequently, the present day and future changes on precipitation conditions were examined using large-scale data from the atmospheric general circulation model HadAM3P to the statistical model. The downscaled climate change signal for both precipitation and raindays, partly for winter and especially for spring, is similar to the signal from the HadAM3P direct ouput: a decrease of the parameters is predicted over the study area. However, the amplitude of the changes was different. Copyright © 2006 Royal Meteorological Society