Poly[tetraaqua-μ4-squarato-di-μ3-squarato-disam­arium(III)]

The structure of the title compound, [Sm2(C4O4)3(H2O)4]n, consists of infinite-chain structural units, built from edge-sharing samarium SmO7(H2O)2 polyhedra and linked via bis-monodendate squarate (sq1) groups. The chains extend along [100] in a zigzag mode and are interconnected by bis-chelating squarate (sq2) ligands into layers parallel to (101). Inter­layer hydrogen bonds strengthen the cohesion of the three-dimensional network. The samarium cation is coordinated by four O atoms from sq1 units and three O atoms from sq2 units, in addition to two water O atoms. The best representation of the samarium SmO7(H2O)2 polyhedron is distorted tricapped trigonal-prismatic. The sq1 ligand has one metal-free O atom and relates three Sm atoms in a bis-monodentate and chelation fashion, the second squarate, sq2, is strictly centrosymmetric and acts as a bis-chelating ligand

A General Probabilistic Forecasting Framework for Offshore Wind Power Fluctuations

Accurate wind power forecasts highly contribute to the integration of wind power into power systems. The focus of the present study is on large-scale offshore wind farms and the complexity of generating accurate probabilistic forecasts of wind power fluctuations at time-scales of a few minutes. Such complexity is addressed from three perspectives: (i) the modeling of a nonlinear and non-stationary stochastic process; (ii) the practical implementation of the model we proposed; (iii) the gap between working on synthetic data and real world observations. At time-scales of a few minutes, offshore fluctuations are characterized by highly volatile dynamics which are difficult to capture and predict. Due to the lack of adequate on-site meteorological observations to relate these dynamics to meteorological phenomena, we propose a general model formulation based on a statistical approach and historical wind power measurements only. We introduce an advanced Markov Chain Monte Carlo (MCMC) estimation method to account for the different features observed in an empirical time series of wind power: autocorrelation, heteroscedasticity and regime-switching. The model we propose is an extension of Markov-Switching Autoregressive (MSAR) models with Generalized AutoRegressive Conditional Heteroscedastic (GARCH) errors in each regime to cope with the heteroscedasticity. Then, we analyze the predictive power of our model on a one-step ahead exercise of time series sampled over 10 min intervals. Its performances are compared to state-of-the-art models and highlight the interest of including a GARCH specification for density forecasts

17O NMR study of the intrinsic magnetic susceptibility and spin dynamics of the quantum kagome antiferromagnet ZnCu3(OH)6Cl2

We report through 17O NMR, an unambiguous local determination of the intrinsic kagome lattice spin susceptibility as well as that created around non-magnetic defects issued from natural Zn/ Cu exchange in the S=1/2 (Cu2+) herbertsmithite ZnCu3(OH)6Cl2 compound. The issue of a singlet-triplet gap is addressed. The magnetic response around a defect is found to markedly differ from that observed in non-frustrated antiferromagnetic materials. Finally, we discuss our relaxation measurements in the light of Cu and Cl NMR data [cond-mat 070314] and suggest a flat q-dependence of the excitations.Comment: Accepted for publication in Phys. Rev. Lett., 3 jan. 2008 Figure 1 has been modified to include a two-components fit of the 17O NMR spectru

The highly conserved serine threonine kinase StkP of Streptococcus pneumoniae contributes to penicillin susceptibility independently from genes encoding penicillin-binding proteins

<p>Abstract</p> <p>Background</p> <p>The serine/threonine kinase StkP of <it>Streptococcus pneumoniae </it>is a major virulence factor in the mouse model of infection. StkP is a modular protein with a N-terminal kinase domain a C-terminal PASTA domain carrying the signature of penicillin-binding protein (PBP) and prokaryotic serine threonine kinase. In laboratory cultures, one target of StkP is the phosphoglucosamine mutase GlmM involved in the first steps of peptidoglycan biosynthesis. In order to further elucidate the importance of StkP in <it>S. pneumoniae</it>, its role in resistance to β-lactams has been assessed by mutational analysis in laboratory cultures and its genetic conservation has been investigated in isolates from infected sites (virulent), asymptomatic carriers, susceptible and non-susceptible to β-lactams.</p> <p>Results</p> <p>Deletion replacement mutation in <it>stkP </it>conferred hypersensitivity to penicillin G and was epistatic on mutations in PBP2X, PBP2B and PBP1A from the resistant 9V clinical isolate URA1258. Genetic analysis of 55 clinical isolates identified 11 StkP alleles differing from the reference R6 allele. None relevant mutation in the kinase or the PASTA domains were found to account for susceptibility of the isolates. Rather the minimal inhibitory concentration (MIC) values of the strains appeared to be determined by their PBP alleles.</p> <p>Conclusion</p> <p>The results of genetic dissection analysis in lab strain Cp1015 reveal that StkP is involved in the bacterial response to penicillin and is epistatic on mutations PBP 2B, 2X and 1A. However analysis of the clinical isolates did not allow us to find the StkP alleles putatively involved in determining the virulence or the resistance level of a given strain, suggesting a strong conservation of StkP in clinical isolates.</p