Subject-specific finite element modelling of the human hand complex : muscle-driven simulations and experimental validation

This paper aims to develop and validate a subject-specific framework for modelling the human hand. This was achieved by combining medical image-based finite element modelling, individualized muscle force and kinematic measurements. Firstly, a subject-specific human hand finite element (FE) model was developed. The geometries of the phalanges, carpal bones, wrist bones, ligaments, tendons, subcutaneous tissue and skin were all included. The material properties were derived from in-vivo and in-vitro experiment results available in the literature. The boundary and loading conditions were defined based on the kinematic data and muscle forces of a specific subject captured from the in-vivo grasping tests. The predicted contact pressure and contact area were in good agreement with the in-vivo test results of the same subject, with the relative errors for the contact pressures all being below 20%. Finally, sensitivity analysis was performed to investigate the effects of important modelling parameters on the predictions. The results showed that contact pressure and area were sensitive to the material properties and muscle forces. This FE human hand model can be used to make a detailed and quantitative evaluation into biomechanical and neurophysiological aspects of human hand contact during daily perception and manipulation. The findings can be applied to the design of the bionic hands or neuro-prosthetics in the future

Scaling behavior of temperature-dependent thermopower in CeAu2Si2 under pressure

We report a combined study of in-plane resistivity and thermopower of the pressure-induced heavy fermion superconductor CeAu2Si2 up to 27.8 GPa. It is found that thermopower follows a scaling behavior in T/T* almost up to the magnetic critical pressure pc ~ 22 GPa. By comparing with resistivity results, we show that the magnitude and characteristic temperature dependence of thermopower in this pressure range are governed by the Kondo coupling and crystal-field splitting, respectively. Below pc, the superconducting transition is preceded by a large negative thermopower minimum, suggesting a close relationship between the two phenomena. Furthermore, thermopower of a variety of Ce-based Kondo-lattices with different crystal structures follows the same scaling relation up to T/T* ~ 2.Comment: 6 pages, 4 figures. Supplementary Material available on reques

Effect of disorder on the pressure-induced superconducting state of CeAu2Si2

CeAu2Si2 is a newly discovered pressure-induced heavy fermion superconductor which shows very unusual interplay between superconductivity and magnetism under pressure. Here we compare the results of high-pressure measurements on single crystalline CeAu2Si2 samples with different levels of disorder. It is found that while the magnetic properties are essentially sample independent, superconductivity is rapidly suppressed when the residual resistivity of the sample increases. We show that the depression of bulk Tc can be well understood in terms of pair breaking by nonmagnetic disorder, which strongly suggests an unconventional pairing state in pressurized CeAu2Si2. Furthermore, increasing the level of disorder leads to the emergence of another phase transition at T* within the magnetic phase, which might be in competition with superconductivity.Comment: 7 pages, 7 figure

Possibility of Unconventional Pairing Due to Coulomb Interaction in Fe-Based Pnictide Superconductors: Perturbative Analysis of Multi-Band Hubbard Models

Possibility of unconventional pairing due to Coulomb interaction in iron-pnictide superconductors is studied by applying a perturbative approach to realistic 2- and 5-band Hubbard models. The linearized Eliashberg equation is solved by expanding the effective pairing interaction perturbatively up to third order in the on-site Coulomb integrals. The numerical results for the 5-band model suggest that the eigenvalues of the Eliashberg equation are sufficiently large to explain the actual high Tc for realistic values of Coulomb interaction and the most probable pairing state is spin-singlet s-wave without any nodes just on the Fermi surfaces, although the superconducting order parameter changes its sign between the small Fermi pockets. On the other hand the 2-band model is quite insufficient to explain the actual high Tc.Comment: 2 pages, 3 figures. Proceedings of the Intl. Symposium on Fe-Oxypnictide Superconductors (Tokyo, 28-29th June 2008

Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO

Following the discovery of superconductivity in an iron-based arsenide LaO1-xFxFeAs with a superconducting transition temperature (Tc) of 26 K[1], Tc was pushed up surprisingly to above 40 K by either applying pressure[2] or replacing La with Sm[3], Ce[4], Nd[5] and Pr[6]. The maximum Tc has climbed to 55 K, observed in SmO1-xFxFeAs[7, 8] and SmFeAsO1-x[9]. The value of Tc was found to increase with decreasing lattice parameters in LnFeAsO1-xFx (Ln stands for the lanthanide elements) at an apparently optimal doping level. However, the F- doping in GdFeAsO is particularly difficult[10,11] due to the lattice mismatch between the Gd2O2 layers and Fe2As2 layers. Here we report observation of superconductivity with Tc as high as 56 K by the Th4+ substitution for Gd3+ in GdFeAsO. The incorporation of relatively large Th4+ ions relaxes the lattice mismatch, hence induces the high temperature superconductivity.Comment: 4 pages, 3 figure

Multiple Superconducting Gaps, Anisotropic Spin Fluctuations and Spin-Orbit Coupling in Iron-Pnictides

This article reviews the NMR and NQR studies on iron-based high-temperature superconductors by the IOP/Okayama group. It was found that the electron pairs in the superconducting state are in the spin-singlet state with multiple fully-opened energy gaps. The antiferromagnetic spin fluctuations in the normal state are found to be closely correlated with the superconductivity. Also the antiferromagnetic spin fluctuations are anisotropic in the spin space, which is different from the case in copper oxide superconductors. This anisotropy originates from the spin-orbit coupling and is an important reflection of the multiple-bands nature of this new class of superconductors.Comment: 20 pages, 16 figure