Periodic ab initio estimates of the dispersive interaction between molecular nitrogen and a monolayer of hexagonal BN

The ab initio determination of the leading long-range term of pairwise additive dispersive interactions, based on the independent analysis of the response properties of the interacting objects, is here considered in the case where these are part of a periodic system. The interaction of a nitrogen molecule with a thin film of hexagonal BN has been chosen as a case study for identifying some of the problems involved, and for proposing techniques for their solution. In order to validate the results so obtained, the interaction energy between N2 and a BN monolayer at different distances has been estimated following a totally different approach, namely by performing post-Hartree–Fock (MP2) supercell calculations using the CRYSTAL+CRYSCOR suite of programs. The results obtained with the two approaches closely agree over a long range, while the limit of validity of the purely dispersive regime can be clearly assessed

Mesoscale variability of water masses in the Arabian Sea as revealed by ARGO floats

By analysing ARGO float data over the last four years, a few aspects of the mesoscale variability of water masses in the Arabian Sea are described. <br><br> The Red Sea Outflow Water (RSOW) is concentrated in the Southwestern Gulf of Aden, in particular when a cyclonic gyre predominates in this region. Salinities of 36.5 and temperatures of 16 °C are found in this area at depths between 600 and 1000 m. RSOW is more dilute in the eastern part of the Gulf, where intense and relatively barotropic gyres mix it with Indian ocean Central Water. RSOW is also detected along the northeastern coast of Socotra, and fragments of RSOW are found between one and three degrees of latitude north of this island. In the whole Gulf of Aden, the correlation between the deep motions of the floats and the sea-level anomaly measured by altimetry is strong, at regional scale. The finer scale details of the float trajectories are not sampled by altimetry and are often related to the anomalous water masses that the floats encounter. <br><br> The Persian Gulf Water (PGW) is found in the float profiles near Ras ash Sharbatat (near 57° E, 18° N), again with 36.5 in salinity and about 18–19 °C in temperature. These observations were achieved in winter when the southwestward monsoon currents can advect PGW along the South Arabian coast. Fragments of PGW were also observed in the Arabian Sea between 18 and 20° N and 63 and 65° E in summer, showing that this water mass can escape the Gulf of Oman southeastward, during that season. <br><br> Kinetic energy distributions of floats with respect to distance or angle share common features between the two regions (Gulf of Aden and Arabian Sea), in particular peaks at 30, 50 and 150 km scales and along the axis of monsoon currents. Hydrological measurements by floats are also influenced by the seasonal variations of PGW and RSOW in these regions

On Stochastic Perturbation Method for Estimation of High Dimensional Matrix

SECTION 1 ROBUST AND MULTIVARIATE DATA ANALYSI

On adaptive filtering for high dimensional systems under parameter uncertainty and its application to satellite data assimilation in oceanography

In this paper, the adaptive filtering theory, recently proposed and developed the authors of present work [1-9] for stochastic, encountered in the field of data as simulation in meteorology and oceanography, is reviewed. Several important questions on numerical estimation og the gain matrix, model reduction, structural  choices for the gain, filter stability… are discussed. We show the connections of present approach with a standard Kalman filtering. Adaptive filter is implemented along with a Kalman filtering. Adaptive filter is implemented along with a Kalman filter and standard Newton relation method on the four-layer adiabatic Miami Isopycnical Co-ordinate Ocean Model (MICOM) to produce the estimate for the deep oceanic circulation using assimilate synthetic observations of surface height. Numerical results justify high efficiency of the adaptive filter whose performance is slightly better than that of a Kalman filter due to  impossibility to correctly specify the error statistics in a Kalman filter

On the structural, electronic and magnetic properties of MnCr2O4 spinel.

International audienceThe structural, electronic and magnetic properties of the MnCr2O4 spinel are investigated using the periodic ab initio Hartree - Fock program CRYSTAL. The geometry is fully optimized and the bulk modulus evaluated. The system is a large-gap insulator; the Mn - O bond is fully ionic, whereas in the Cr - O case there is a relatively large overlap between the Cr d and the O sp orbitals, and the resulting bond has some covalent character. The ferromagnetic solution (all spins in the same direction) and two ferrimagnetic solutions (one or two Mn atoms of the unit cell with spin down, the remaining transition metal atoms with spin up) have been considered; the latter are more stable than the former by 2.2 and 3.8 mHartree per unit cell, respectively. At zero pressure, the spinel is more stable than the mixture of simple oxides MnO + α-Cr2O3 by about , in excellent agreement with experiment

Mesoscale variability in the Arabian Sea from HYCOM model results and observations: impact on the Persian Gulf Water path

The Arabian Sea and Sea of Oman circulation and water masses, subject to monsoon forcing, reveal a strong seasonal variability and intense mesoscale features. We describe and analyze this variability and these features, using both meteorological data (from ECMWF reanalyses), in situ observations (from the ARGO float program and the GDEM - Generalized Digital Environmental mode - climatology), satellite altimetry (from AVISO) and a regional simulation with a primitive equation model (HYCOM - the Hybrid Coordinate Ocean Model). The model and observations display comparable variability, and the model is then used to analyze the three-dimensional structure of eddies and water masses with higher temporal and spatial resolutions than the available observations. The mesoscale features are highly seasonal, with the formation of coastal currents, destabilizing into eddies, or the radiation of Rossby waves from the Indian coast. The mesoscale eddies have a deep dynamical influence and strongly drive the water masses at depth. In particular, in the Sea of Oman, the Persian Gulf Water presents several offshore ejection sites and a complex recirculation, depending on the mesoscale eddies. The associated mechanisms range from coastal ejection via dipoles, alongshore pulses due to a cyclonic eddy, to the formation of lee eddies downstream of Ra's Al Hamra. This water mass is also captured inside the eddies via several mechanisms, keeping high thermohaline characteristics in the Arabian Sea. The variations of the outflow characteristics near the Strait of Hormuz are compared with variations downstream

DL_POLY_2 adaptations for solvation studies

International audienceAdaptations of the mol. dynamics engine DL_POLY\₂ were recently made to facilitate the investigation of questions arising mainly in the study of solvation dynamics. This paper presents the new facilities, with consideration of practical points for their efficient use and illustrative results obtained with them. Supplementary Information provides further details of their implementation to encourage future improvements and extensions. The adaptations of DL_POLY\₂ for solvation studies are: species by species and inter-species breakdown of the total energy for systems contg. several species, such as solns. or models of adsorption, with, as an illustration, diffusion of a particular water mol. in a microporous silica zeolite, silicalite. The new facilities allow correlation of the trajectory of the mol. with its interaction with the host matrix. Solvation-induced spectral shifts, illustrated by the absorption shift and Stokes shift of a cyanoarom. dye in soln. in methanol. We discuss the relative importance of different contributions to the total spectral shift. Free energies by thermodn. integration, illustrated by calcn. of the excess free energy of liq. dimethylsulfoxide. We examine the use of different weighting functions for the mixed Hamiltonian to avoid or to delay divergence in thermodn. integration

Dysregulated CRTC1 activity is a novel component of PGE2 signaling that contributes to colon cancer growth

First identified as a dedicated CREB (cAMP response element-binding protein) co-activator, CRTC1 (CREB-regulated transcription co-activator 1) has been widely implicated in various neuronal functions because of its predominant expression in the brain. However, recent evidences converge to indicate that CRTC1 is aberrantly activated in an expanding number of adult malignancies. In this study, we provide strong evidences of enhanced CRTC1 protein content and transcriptional activity in mouse models of sporadic (APC(min/+) mice) or colitis-associated colon cancer azoxymethane/dextran sulfate sodium (AOM/DSS-treated mice), and in human colorectal tumors specimens compared with adjacent normal mucosa. Among signals that could trigger CRTC1 activation during colonic carcinogenesis, we demonstrate that treatment with cyclooxygenase 2 (COX2) inhibitors reduced nuclear CRTC1 active form levels in colonic tumors of APC(min/+) or AOM/DSS mice. In accordance, prostaglandins E2 (PGE2) exposure to human colon cancer cell lines promoted CRTC1 dephosphorylation and parallel nuclear translocation, resulting in enhanced CRTC1 transcriptional activity, through EP1 and EP2 receptors signaling and consecutive calcineurin and protein kinase A activation. In vitro CRTC1 loss of function in colon cancer cell lines was associated with reduced viability and cell division rate as well as enhanced chemotherapy-induced apoptosis on PGE2 treatment. Conversely, CRTC1 stable overexpression significantly increased colonic xenografts tumor growth, therefore demonstrating the role of CRTC1 signaling in colon cancer progression. Identification of the transcriptional program triggered by enhanced CRTC1 expression during colonic carcinogenesis, revealed some notable pro-tumorigenic CRTC1 target genes including NR4A2, COX2, amphiregulin (AREG) and IL-6. Finally, we demonstrate that COX2, AREG and IL-6 promoter activities triggered by CRTC1 are dependent on functional AP1 and CREB transcriptional partners. Overall, our study establishes CRTC1 as new mediator of PGE2 signaling, unravels the importance of its dysregulation in colon cancer and strengthens its use as a bona fide cancer marker