Synthesis,structure and magnetic properties of a novel Tb4 spin cluster and synthesis of a Tb chain

The syntheses of two new polynuclear Tb^III compounds are reported. A tetranuclear complex [Tb₄(H₂L)₂(H₄L)₂(OAc)₈] (1), with H₄L = 2-((2-hydroxy-benzylidene)-amino)-2-hydroxy-methyl-propane-1,3-diol, has a butterfly-type structure, while [Tb(OAc)₃MeOH]_∞ (2) is a linear chain. A novel binding mode for H₂L²⁻ is observed in 1, with two alkoxides each bridging three Tb^III ions. The magnetic properties of 1 are determined by the superposition of the ligand field split ⁷F₆ states of Tb^III single-ions located on two crystallographically distinct sites. Weak antiferromagnetic exchange interactions possibly contribute to the lowering of the magnetic moment at the lowest temperatures.     

Temperature dependant polycrystal model application to bainitic steel behavior under tri-axial loading in the ductile–brittle transition

A polycrystal finite element (FE) model describing the temperature evolution of low carbon steel is proposed in order to forecast the local mechanical fields as a function of temperature, for bainitic microstructure submitted to tri-axial loading. The model is designed for finite strains, large lattice rotations and temperatures ranging into the brittle–ductile transition domain. The dislocation densities are the internal variables. At low temperature in Body Centred Cubic (BCC) materials, plasticity is governed by double kink nucleation of screw dislocations, whereas at high temperature, plasticity depends on interactions between mobile dislocations and the forest dislocations. In this paper, the constitutive law and the evolution of the dislocation densities are written as a function of temperature and describe low and high temperature mechanisms. The studied aggregates are built from Electron Back Scattering Diffraction (EBSD) images of real bainitic steel. The aggregate is submitted to a tri-axial loading in order to describe the material at a crack tip. Mechanical parameters are deduced from mechanical tests. The local strain and stress fields, computed for different applied loadings, present local variations which depend on temperature and on tri-axial ratio. The distribution curves of the maximal principal stresses show that heterogeneities respectively increase with temperature and decrease with tri-axial ratio. A direct application of this model provides the evaluation of the rupture probability within the aggregate, which is treated as the elementary volume in the weak link theory. A comparison with the Beremin criterion calibrated on experimental data, shows that the computed fracture probability dispersion induced by the stress heterogeneities is of the same order than the measured dispersion. Temperature and stress tri-axiality ratio effects are also investigated. It is shown that these two parameters have a strong effect on fracture owing to their influence on the heterogeneous plastic strain. These inhomogeneities can initiate cleavage fracture.     

The generation of a novel polyoxometalate-based 3D framework following picolinate-chelation of tungsten and potassium centres

A new polyoxometalate-based 3D framework K(5)Na[K(2){Dy(H(2)O)(3)}(2){As(2)W(19)O(68)}{WO(2)(pic)}(2)] (1) (pic = 2-picolinate), composed of picolinate-functionalised dysprosium-containing tungstoarsenates and distorted potassium-picolinate cubane units, has been synthesised from the polyoxometalate precursor [As(2)W(19)O(67)(H(2)O)](14-).     

Solving the biharmonic Dirichlet problem on domains with corners

The biharmonic Dirichlet boundary value problem on a bounded domain is the focus of the present paper. By Riesz' representation theorem the existence and uniqueness of a weak solution is quite direct. The problem that we are interested in appears when one is looking for constructive approximations of a solution. Numerical methods using for example finite elements, prefer systems of second equations to fourth order problems. Ciarlet and Raviart in 7 and Monk in 21 consider approaches through second order problems assuming that the domain is smooth. We will discuss what happens when the domain has corners. Moreover, we will suggest a setting, which is in some sense between Ciarlet‐Raviart and Monk, that inherits the benefits of both settings and that will give the weak solution through a system type approach.     

Sunburn Risk Among Children and Outdoor Workers in South Africa and Reunion Island Coastal Sites

To estimate potential sunburn risk for schoolchildren and outdoor workers, ground‐based ambient solar ultraviolet radiation (UVR) measurements were converted into possible child (5% of ambient solar UVR) and outdoor worker (20% of ambient solar UVR) solar UVR exposures by skin type and season for three coastal sites: Durban, Cape Point (South Africa) and Saint Denis (Reunion Island, France). Cumulative daily ambient solar UVR levels were relatively high at all sites, especially during summer, with maximum values of about 67, 57 and 74 Standard Erythemal Dose (SED) (1 SED = 100 J m^?2) at Durban, Cape Point and Saint Denis respectively. Sunburn risk was evident for both children and outdoor workers, especially those with skin types I and II (extremely to moderately sensitive) during summer, early autumn and/or late spring at all three sites. Although results need to be verified with real‐time, instantaneous and nonintegrated personal solar UVR measurements, this understanding of sunburn risk is useful for initiating the development skin cancer prevention and sun protection awareness campaigns in both countries.