4,490 research outputs found

    Electronic density of states derived from thermodynamic critical field curves for underdoped La-Sr-Cu-O

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    Thermodynamic critical field curves have been measured for La2xSrxCuO4+δLa_{2-x}Sr_{x}CuO_{4+\delta} over the full range of carrier concentrations where superconductivity occurs in order to determine changes in the normal state density of states with carrier concentration. There is a substantial window in the HTH-T plane where the measurements are possible because the samples are both thermodynamically reversible and the temperature is low enough that vortex fluctuations are not important. In this window, the data fit Hao-Clem rather well, so this model is used to determine HcH_c and κc\kappa_c for each temperature and carrier concentration. Using N(0) and the ratio of the energy gap to transition temperature, Δ(0)/kBTc\Delta (0)/k_BT_c, as fitting parameters, the HcvsTH_c vs T curves give Δ(0)/kBTc2.0\Delta (0)/k_BT_c \sim 2.0 over the whole range of xx. Values of N(0) remain rather constant in the optimum-doped and overdoped regime, but drops quickly toward zero in the underdoped regime.

    A semi-small decomposition of the Chow ring of a matroid

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    We give a semi-small orthogonal decomposition of the Chow ring of a matroid M. The decomposition is used to give simple proofs of Poincar\'e duality, the hard Lefschetz theorem, and the Hodge-Riemann relations for the Chow ring, recovering the main result of [AHK18]. We also show that a similar semi-small orthogonal decomposition holds for the augmented Chow ring of M

    Emerging sensor-cloud technology for pervasive services and applications

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    This is an Editorial article for the Special Issue on "Emerging Sensor-Cloud Technology for Pervasive Services and Applications" of the International Journal of Distributed Sensor Networks

    Influence of Mg Deficiency on the Superconductivity in MgB2 Thin Films Grown by using HPCVD

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    The effects of Mg deficiency in MgB2 films grown by using hybrid physical-chemical vapor deposition were investigated after vacuum annealing at various temperatures. High-quality MgB2 films grown on c-cut Al2O3 substrates with different superconducting transition temperatures (Tc) of 40.2 and 41 K were used in this study. As the annealing temperature was increased from 200 to 800 C, the Mg contents in the MgB2 films systemically decreased, but the Tc's did not change, within 0.12 K, until the annealing temperature reached 700 C. For MgB2 films annealed at 800 C for 30 min, however, no superconductivity was observed, and the temperature dependence of the resistivity showed a semiconducting behavior. We also found that the residual resistivity ratio decreased with increasing annealing temperature.Comment: 7 pages including 4 figure

    Dynamic Simulation for Zero-Gravity Activities

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    Working and training for space activities is difficult in terrestrial environments. We approach this crucial aspect of space human factors through 3D computer graphics dynamics simulation of crewmembers, their tasks, and physics-based movement modeling. Such virtual crewmembers may be used to design tasks and analyze their physical workload to maximize success and safety without expensive physical mockups or partially realistic neutral-buoyancy tanks. Among the software tools we have developed are methods for fully articulated 3D human models and dynamic simulation. We are developing a fast recursive dynamics algorithm for dynamically simulating articulated 3D human models, which comprises kinematic chains - serial, closed-loop, and tree-structure - as well as the inertial properties of the segments. Motion planning is done by first solving the inverse kinematic problem to generate possible trajectories, and then by solving the resulting nonlinear optimal control problem. For example, the minimization of the torques during a simulation under certain constraints is usually applied and has its origin in the biomechanics literature. Examples of space activities shown are zero-gravity self orientation and ladder traversal. Energy expenditure is computed for the traversal task

    Modulated structures in electroconvection in nematic liquid crystals

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    Motivated by experiments in electroconvection in nematic liquid crystals with homeotropic alignment we study the coupled amplitude equations describing the formation of a stationary roll pattern in the presence of a weakly-damped mode that breaks isotropy. The equations can be generalized to describe the planarly aligned case if the orienting effect of the boundaries is small, which can be achieved by a destabilizing magnetic field. The slow mode represents the in-plane director at the center of the cell. The simplest uniform states are normal rolls which may undergo a pitchfork bifurcation to abnormal rolls with a misaligned in-plane director.We present a new class of defect-free solutions with spatial modulations perpendicular to the rolls. In a parameter range where the zig-zag instability is not relevant these solutions are stable attractors, as observed in experiments. We also present two-dimensionally modulated states with and without defects which result from the destabilization of the one-dimensionally modulated structures. Finally, for no (or very small) damping, and away from the rotationally symmetric case, we find static chevrons made up of a periodic arrangement of defect chains (or bands of defects) separating homogeneous regions of oblique rolls with very small amplitude. These states may provide a model for a class of poorly understood stationary structures observed in various highly-conducting materials ("prechevrons" or "broad domains").Comment: 13 pages, 13 figure
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