61 research outputs found
Glacial isostatic adjustment associated with the Barents Sea ice sheet: a modelling inter-comparison
The 3D geometrical evolution of the Barents Sea Ice Sheet (BSIS), particularly during its late-glacial retreat phase, remains largely ambiguous due to the paucity of direct marine- and terrestrial-based evidence constraining its horizontal and vertical extent and chronology. One way of validating the numerous BSIS reconstructions previously proposed is to collate and apply them under a wide range of Earth models and to compare prognostic (isostatic) output through time with known relative sea-level (RSL) data. Here we compare six contrasting BSIS load scenarios via a spherical Earth system model and derive a best-fit, χ2 parameter using RSL data from the four main terrestrial regions within the domain: Svalbard, Franz Josef Land, Novaya Zemlya and northern Norway. Poor χ2 values allow two load scenarios to be dismissed, leaving four that agree well with RSL observations. The remaining four scenarios optimally fit the RSL data when combined with Earth models that have an upper mantle viscosity of 0.2–2 × 1021 Pa s, while there is less sensitivity to the lithosphere thickness (ranging from 71 to 120 km) and lower mantle viscosity (spanning 1–50 × 1021 Pa s). GPS observations are also compared with predictions of present-day uplift across the Barents Sea. Key locations where relative sea-level and GPS data would prove critical in constraining future ice-sheet modelling efforts are also identified
Differential Regulation of Ceruloplasmin Isoforms Expression in Macrophages and Hepatocytes
Prémio de melhor poster.Ceruloplasmin (Cp) is an acute-phase protein that has been implicated in iron metabolism due to its ferroxidase activity, assisting ferroportin (Fpn) on cellular iron efflux. However, Cp exhibits both anti- and pro-oxidant activities and its physiological functions remain unclear. Cp can be expressed as a secreted or as a membrane glycosylphosphatidylinositol-anchored protein (GPI-Cp), this latter one being mostly expressed in the brain. Herein, we studied the expression of both Cp isoforms in human peripheral blood lymphocytes, monocytes, mouse macrophages and human hepatocarcinoma cell line HepG2, using immunofluorescence and immunoblotting techniques. Co-localization of Cp and Fpn was also investigated by immunofluorescence in mouse macrophages.
Cp was detected by immunoblotting and immunofluorescence in membrane and cytosol of all cells types studied. The Cp detected at cell surface was identified as the GPI-isoform by PI-PLC test and shown to localize in lipid rafts in monocytes, macrophages and HepG2 cells. In macrophages, increased expression levels and co-localization of Fpn and GPI-Cp at cell surface lipid rafts were observed after iron treatment. Such upregulation of Cp by iron was not observed in HepG2 cells.
Our results revealed an unexpected ubiquitous expression of the GPI-Cp isoform in immune and hepatic cells. A differential regulation of Cp in these cells may reflect distinct physiological functions of this oxidase according to cell-type specificity. In macrophages, GPI-Cp and Fpn likely interact in lipid rafts to export iron. A better insight into the expression of both Cp isoforms in different cell types will help to clarify its role in many diseases related to iron metabolism, inflammation and oxidative biology.This work was supported by National Institute of Health Dr Ricardo Jorge, I.P (Grants BID 02/2006-I and BIC/07/2004-IV), INSERM (Institut National de la Santé et de la Recherche Médicale), CNRS (Centre National de la Recherche
Scientifique), ANR (Agence Nationale de la Recherche, France; ANR- 08-GENO-000) and Luso-French Integrated Actions 2008-2009 (F-28/08 and F-21/09) and by Fundação para a Ciência e Tecnologia (Grant
SFRH/BD/48671/200
Holonomic functions of several complex variables and singularities of anisotropic Ising n-fold integrals
Lattice statistical mechanics, often provides a natural (holonomic) framework
to perform singularity analysis with several complex variables that would, in a
general mathematical framework, be too complex, or could not be defined.
Considering several Picard-Fuchs systems of two-variables "above" Calabi-Yau
ODEs, associated with double hypergeometric series, we show that holonomic
functions are actually a good framework for actually finding the singular
manifolds. We, then, analyse the singular algebraic varieties of the n-fold
integrals , corresponding to the decomposition of the magnetic
susceptibility of the anisotropic square Ising model. We revisit a set of
Nickelian singularities that turns out to be a two-parameter family of elliptic
curves. We then find a first set of non-Nickelian singularities for and , that also turns out to be rational or ellipic
curves. We underline the fact that these singular curves depend on the
anisotropy of the Ising model. We address, from a birational viewpoint, the
emergence of families of elliptic curves, and of Calabi-Yau manifolds on such
problems. We discuss the accumulation of these singular curves for the
non-holonomic anisotropic full susceptibility.Comment: 36 page
Random Matrix Theory and higher genus integrability: the quantum chiral Potts model
We perform a Random Matrix Theory (RMT) analysis of the quantum four-state
chiral Potts chain for different sizes of the chain up to size L=8. Our
analysis gives clear evidence of a Gaussian Orthogonal Ensemble statistics,
suggesting the existence of a generalized time-reversal invariance.
Furthermore a change from the (generic) GOE distribution to a Poisson
distribution occurs when the integrability conditions are met. The chiral Potts
model is known to correspond to a (star-triangle) integrability associated with
curves of genus higher than zero or one. Therefore, the RMT analysis can also
be seen as a detector of ``higher genus integrability''.Comment: 23 pages and 10 figure
First-order transition features of the 3D bimodal random-field Ising model
Two numerical strategies based on the Wang-Landau and Lee entropic sampling
schemes are implemented to investigate the first-order transition features of
the 3D bimodal () random-field Ising model at the strong disorder
regime. We consider simple cubic lattices with linear sizes in the range
and simulate the system for two values of the disorder strength:
and . The nature of the transition is elucidated by applying the
Lee-Kosterlitz free-energy barrier method. Our results indicate that, despite
the strong first-order-like characteristics, the transition remains continuous,
in disagreement with the early mean-field theory prediction of a tricritical
point at high values of the random-field.Comment: 19 pages, 6 figures, slightly extended version as accepted for
publicatio
Phase Diagram of the 3D Bimodal Random-Field Ising Model
The one-parametric Wang-Landau (WL) method is implemented together with an
extrapolation scheme to yield approximations of the two-dimensional
(exchange-energy, field-energy) density of states (DOS) of the 3D bimodal
random-field Ising model (RFIM). The present approach generalizes our earlier
WL implementations, by handling the final stage of the WL process as an
entropic sampling scheme, appropriate for the recording of the required
two-parametric histograms. We test the accuracy of the proposed extrapolation
scheme and then apply it to study the size-shift behavior of the phase diagram
of the 3D bimodal RFIM. We present a finite-size converging approach and a
well-behaved sequence of estimates for the critical disorder strength. Their
asymptotic shift-behavior yields the critical disorder strength and the
associated correlation length's exponent, in agreement with previous estimates
from ground-state studies of the model.Comment: 18 pages, 7 figure
Critical aspects of the random-field Ising model
We investigate the critical behavior of the three-dimensional random-field Ising model
(RFIM) with a Gaussian field distribution at zero temperature. By implementing a
computational approach that maps the ground-state of the RFIM to the maximum-flow
optimization problem of a network, we simulate large ensembles of disorder realizations of
the model for a broad range of values of the disorder strength h and
system sizes  = L3, with L ≤ 156. Our averaging procedure
outcomes previous studies of the model, increasing the sampling of ground states by a
factor of 103. Using well-established finite-size scaling schemes, the
fourth-order’s Binder cumulant, and the sample-to-sample fluctuations of various
thermodynamic quantities, we provide high-accuracy estimates for the critical field
hc, as well as the critical exponents ν,
β/ν, and γ̅/ν of the correlation length, order parameter, and
disconnected susceptibility, respectively. Moreover, using properly defined noise to
signal ratios, we depict the variation of the self-averaging property of the model, by
crossing the phase boundary into the ordered phase. Finally, we discuss the controversial
issue of the specific heat based on a scaling analysis of the bond energy, providing
evidence that its critical exponent α ≈ 0−
Glacial isostatic adjustment associated with the Barents Sea ice sheet: A modelling inter-comparison
Global link between deformation and volcanic eruption quantified by satellite imagery
A key challenge for volcanological science and hazard management is that few of the world’s volcanoes are effectively monitored. Satellite imagery covers volcanoes globally throughout their eruptive cycles, independent of ground-based monitoring, providing a multidecadal archive suitable for probabilistic analysis linking deformation with eruption. Here we show that, of the 198 volcanoes systematically observed for the past 18 years, 54 deformed, of which 25 also erupted. For assessing eruption potential, this high proportion of deforming volcanoes that also erupted (46%), together with the proportion of non-deforming volcanoes that did not erupt (94%), jointly represent indicators with ‘strong’ evidential worth. Using a larger catalogue of 540 volcanoes observed for 3 years, we demonstrate how this eruption–deformation relationship is influenced by tectonic, petrological and volcanic factors. Satellite technology is rapidly evolving and routine monitoring of the deformation status of all volcanoes from space is anticipated, meaning probabilistic approaches will increasingly inform hazard decisions and strategic development
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