528 research outputs found
Corecursive featherweight Java revisited
We describe a Java-like calculus which supports cyclic data structures, and offers a mechanism of flexible regular corecursion for their manipulation. The calculus enhances an earlier proposal by a more sophisticated reduction semantics, which filters out, by an additional check, some spurious results which were obtained in the previous model
Fine-scale thermohaline ocean structure retrieved with 2-D prestack full-waveform inversion of multichannel seismic data: Application to the Gulf of Cadiz (SW Iberia)
18 pages, 9 figures, supporting information https://dx.doi.org/10.1002/2016JC011844This work demonstrates the feasibility of 2-D time-domain, adjoint-state acoustic full-waveform inversion (FWI) to retrieve high-resolution models of ocean physical parameters such as sound speed, temperature and salinity. The proposed method is first described and then applied to prestack multichannel seismic (MCS) data acquired in the Gulf of Cadiz (SW Iberia) in 2007 in the framework of the Geophysical Oceanography project. The inversion strategy flow includes specifically designed data preconditioning for acoustic noise reduction, followed by the inversion of sound speed in the shotgather domain. We show that the final sound speed model has a horizontal resolution of ∼ 70 m, which is two orders of magnitude better than that of the initial model constructed with coincident eXpendable Bathy Thermograph (XBT) data, and close to the theoretical resolution of O(λ). Temperature (T) and salinity (S) are retrieved with the same lateral resolution as sound speed by combining the inverted sound speed model with the thermodynamic equation of seawater and a local, depth-dependent T-S relation derived from regional conductivity-temperature-depth (CTD) measurements of the National Oceanic and Atmospheric Administration (NOAA) database. The comparison of the inverted T and S models with XBT and CTD casts deployed simultaneously to the MCS acquisition shows that the thermohaline contrasts are resolved with an accuracy of 0.18oC for temperature and 0.08 PSU for salinity. The combination of oceanographic and MCS data into a common, pseudo-automatic inversion scheme allows to quantitatively resolve submeso-scale features that ought to be incorporated into larger-scale ocean models of oceans structure and circulationThe work has been partially supported by the projects KALEIDOSCOPE and CO-Dos financed by REPSOL and MINECO project POSEIDON (CTM2010-21569) and HADES (CTM2011-30400-C02). B. Biescas work has been funded by the European Commission through the Marie Curie Action FP7-PEOPLE-2012-COFUND-600407Peer Reviewe
Vortex nucleation in mesoscopic Bose superfluid and breaking of the parity symmetry
We analyze vortex nucleation in mezoscopic 2D Bose superfluid in a rotating
trap. We explicitly include a weakly anisotropic stirring potential, breaking
thus explicitly the axial symmetry. As the rotation frequency passes the
critical value the system undergoes an extra symmetry
change/breaking. Well below the ground state is properly described
by the mean field theory with an even condensate wave function. Well above
the MF solution works also well, but the order parameter becomes
odd. This phenomenon involves therefore a discrete parity symmetry breaking. In
the critical region the MF solutions exhibit dynamical instability. The true
many body state is a strongly correlated entangled state involving two
macroscopically occupied modes (eigenstates of the single particle density
operator). We characterize this state in various aspects: i) the eligibility
for adiabatic evolution; ii) its analytical approximation given by the
maximally entangled combination of two single modes; and finally iii) its
appearance in particle detection measurements.Comment: 14 pages, 27 figure
Relationships between phenotypic plasticity and environmental variables.
To understand the relations between environment and phenotypic plasticity is important to forecast any possible adaptation of plants to climate change.
We tested for any difference between central and marginal (Mediterranean and Alpine). Study was performed on 20 populations chosen on the basis of their distance from niche optimum.In Mediterranean marginal populations :
\u2022 wide flowers display corolla,
\u2022 short stamen, inducing more investment in attractiveness than in seed maturation
\u2022 lower pollen production and seed set.
Our results suggestthat: Largest floral display and lowest allocation of resources for seeds production in Mediterranean populations may be due to the highest competition for resources (pollinators, water and soil nutrient) together with the lowest resource availability. Future climate change will probably bring about: extinction of low altitudes populations the upward shift of other
Symmetry breaking in small rotating cloud of trapped ultracold Bose atoms
We study the signatures of rotational and phase symmetry breaking in small
rotating clouds of trapped ultracold Bose atoms by looking at rigorously
defined condensate wave function. Rotational symmetry breaking occurs in narrow
frequency windows, where the ground state of the system has degenerated with
respect to the total angular momentum, and it leads to a complex wave function
that exhibits vortices clearly seen as holes in the density, as well as
characteristic vorticity. Phase symmetry (or gauge symmetry) breaking, on the
other hand, is clearly manifested in the interference of two independent
rotating clouds.Comment: 4 pages, 2 figure
Vortex nucleation as a case study of symmetry breaking in quantum systems
Mean-field methods are a very powerful tool for investigating weakly
interacting many-body systems in many branches of physics. In particular, they
describe with excellent accuracy trapped Bose-Einstein condensates. A generic,
but difficult question concerns the relation between the symmetry properties of
the true many-body state and its mean-field approximation. Here, we address
this question by considering, theoretically, vortex nucleation in a rotating
Bose-Einstein condensate. A slow sweep of the rotation frequency changes the
state of the system from being at rest to the one containing one vortex. Within
the mean-field framework, the jump in symmetry occurs through a turbulent phase
around a certain critical frequency. The exact many-body ground state at the
critical frequency exhibits strong correlations and entanglement. We believe
that this constitutes a paradigm example of symmetry breaking in - or change of
the order parameter of - quantum many-body systems in the course of adiabatic
evolution.Comment: Minor change
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