An Asymptotic Preserving Scheme for the Euler equations in a strong magnetic field

This paper is concerned with the numerical approximation of the isothermal Euler equations for charged particles subject to the Lorentz force. When the magnetic field is large, the so-called drift-fluid approximation is obtained. In this limit, the parallel motion relative to the magnetic field direction splits from perpendicular motion and is given implicitly by the constraint of zero total force along the magnetic field lines. In this paper, we provide a well-posed elliptic equation for the parallel velocity which in turn allows us to construct an Asymptotic-Preserving (AP) scheme for the Euler-Lorentz system. This scheme gives rise to both a consistent approximation of the Euler-Lorentz model when epsilon is finite and a consistent approximation of the drift limit when epsilon tends to 0. Above all, it does not require any constraint on the space and time steps related to the small value of epsilon. Numerical results are presented, which confirm the AP character of the scheme and its Asymptotic Stability

Heat Conduction in κ\kappa-(BEDT-TTF)2_2Cu(NCS)2_2

The first study of thermal conductivity, $\kappa$, in a quasi-two-dimensional organic superconductor of the $\kappa$-(BEDT-TTF)$_2$X family reveals features analogous to those already observed in the cuprates. The onset of superconductivity is associated with a sudden increase in $\kappa$ which can be suppressed by the application of a moderate magnetic field. At low temperatures, a finite linear term - due to a residual electronic contribution- was resolved. The magnitude of this term is close to what is predicted by the theory of transport in unconventional superconductors.Comment: 5 pages, 4 figures include

Three-dimensional lanthanide-organic frameworks based on di-, tetra-, and hexameric clusters

Three-dimensional lanthanide-organic frameworks formulated as (CH3)2NH2[Ln(pydc)2] · 1/2H2O [Ln3+ ) Eu3+ (1a) or Er3+ (1b); pydc2- corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H2pydc)], [Er4(OH)4(pydc)4(H2O)3] ·H2O (2), and [PrIII 2PrIV 1.25O(OH)3(pydc)3] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide - DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction, thermogravimetric analysis, vibrational spectroscopy (FT-IR and FT-Raman), electron microscopy, and CHN elemental analysis. While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction of anionic ∞ 3{[Ln(pydc)2]-} frameworks having the channels filled by the charge-balancing (CH3)2NH2 + cations generated in situ by the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3 contain instead tetrameric [Er4(μ3-OH)4]8+ and hexameric |Pr6(μ3-O)2(μ3-OH)6| clusters which act as the building blocks of the networks, and are bridged by the H2-xpydcx- residues. It is demonstrated that this modular approach is reflected in the topological nature of the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 °C with this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core

A HYBRID METHOD FOR ANISOTROPIC ELLIPTIC PROBLEMS BASED ON THE COUPLING OF AN ASYMPTOTIC-PRESERVINGMETHOD WITH THE ASYMPTOTIC LIMIT MODEL

International audienceThis paper presents a hybrid numerical method to solve efficiently a class of highly anisotropic elliptic problems. The anisotropy is aligned with one coordinate axis and its strength is described by a parameter ε ∈ (0, 1], which can largely vary in the study domain. Our hybrid model is based on asymptotic techniques and couples (spatially) an asymptotic-preserving model with its asymptotic limit model, the latter being used in regions where the anisotropy parameter ε is small. Adequate coupling conditions link the two models. The aim of this hybrid procedure is to reduce the computational time for problems where the region of small ε-values extends over a significant part of the domain, and this is due to the reduced complexity of the limit model

Anomalous flux jump in the organic superconductor K-(BEDT-TTF)2Cu(N(CN)2)Br

International audienceWe study the hysteresis loop of κ-​(BEDT-​TTF)​2Cu(N(CN)​2)​Br as a function of the thermomagnetic history of the sample. The field-​cooled state (fc) always differs radically from that of conventional materials. However, the relaxed magnetization generally coincides with the zero-​field cooled (zfc) value, but the transition toward the zfc state is always preceded by strong fluctuations in the measured magnetization

Synthesis, Crystal Structure and Porosity Estimation of Hydrated Erbium Terephthalate Coordination Polymers.

WOSInternational audienceThe reaction of Er3+ ion with poly-carboxylate ligands in gel media leads to coordination polymers exhibiting various structural types and various dimensionality. Five Er3+ / 1,4-benzenedicarboxylate based coordination polymers have been obtained in such conditions. Four out of five are new. Their crystal structures are reported and compared herein. The compound (1-), namely Er2Ter3(H2O)6, where H2Ter symbolizes the terephtalic acid, crystallizes in the space group (N°2) with a=7.8373(10)Å, b=9.5854(2)Å, c=10.6931(2)Å, a=68.7770(8)°, b=70.8710(8)°, g=75.3330(12)°. It has already been reported elsewhere. The last four compounds are new. The compound (2-), namely Er2Ter3(H2O)6,2H2O crystallizes in the space group (N°14) with a=6.7429(2)Å, b=22.4913(7)Å, c=9.6575(3)Å, b=91.6400(18)°. The compound (3-), namely Er2Ter3(H2O)8,2H2O crystallizes in the space group (N°2) with a=7.5391(2)Å, b=10.0533(3)Å, c=10.4578(3)Å, a=87.7870(10)°, b=82.5510(11)°, g=86.2800(16)°. The compound (4-), namely Er2Ter3(H2O)6,2H2O crystallizes in the space group (N°15) with a=38.5123(13)Å, b=11.1241(4)Å, c=7.0122(2)Å, b=98.634(2)°. The compound (5-), namely Er2Ter3(H2O)6,H2O crystallizes in the space group (N°2) with a=6.8776(10)Å, b=11.0420(2)Å, c=18.5675(3)Å, a=84.7240(6)°, b=81.8380(6)°, g=84.1770(8)°. A computational method has also been developed in order to evaluate the potential porosity of coordination polymers. This method is described then applied to the different Er2Ter3(H2O)n coordination polymers previously described