We present a mechanism for emission of electromagnetic terahertz waves by simulation. High Tc superconductors form naturally stacked Josephson junctions. When an external current and a magnetic field are applied to the sample, fluxon flow induces voltage. The voltage creates oscillating current through the Josephson effect and the current excites the Josephson plasma. The sample works as a cavity, and the input energy is stored in a form of standing wave of the Josephson plasma. A part of the energy is emitted as terahertz waves.PACS numbers: 74.50.+r, 74.25.Gz, 85.25.Cp Continuous coherent terahertz waves have various applications in scientific field such as biology and information science. One of the hurdles for technological advancements in the terahertz region of electromagnetic wave is the development of sources for intense and continuous coherent terahertz waves. Therefore, we investigate a new mechanism for emitting intense continuous and frequency tunable terahertz waves. In the high temperature superconductors, the strongly superconducting CuO 2 layers and insulating layers are alternatively stacked along the c-axis of the crystals and form a naturally multi-connected Josephson junction called intrinsic Josephson junction (IJJ). In the IJJ there appears a new excitation wave called Josephson plasma, the frequency of which is in the range of terahertz 1,2 . The frequency appears in the region inside the superconducting energy gap and the Landau damping is very weak, and thus the excited plasma decays by emitting a terahertz electromagnetic wave.For investigating an emission mechanism of terahertz electromagnetic wave from the IJJ, we use the following model shown by Figure 1. In Fig. 1 the IJJ is shown in green and the electrodes of a normal metal (for example gold) are shown in yellow. An external magnetic field B applied in the direction of the y-axis induces fluxons in the direction. The centers of fluxons are in the insulating layers. In this system, the superconducting and normal currents almost uniformly flow in the direction indicated by J in Fig.1. The fluxons flow in the direction of the x-axis with a velocity v and induce the flow voltage in the direction of the z-axis. These voltages creates the oscillating Josephson current along the z-axis by the Josephson effect, when temperature is low enough below T c and the superconducting current is smaller than the superconducting depairing current along the c-axis. This oscillating current interacts strongly with the Josephson plasma due to the nonlinear nature of the system and intensively excites the Josephson plasma wave as shown later. We use Bi 2 Sr 2 CaCu 2 O 8+δ that is appropriate in the experiments, and apply a magnetic field and external currents around J c the critical current to the IJJ. Then, the frequency of the plasma waves appears in the terahertz frequency range. The plasma wave is converted to an intense terahertz electromagnetic wave in the waveguide (dielectric) shown in orange in Fig. 1.In accordance with the mechanism mention...

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GeoFEM has been developed as a finite element solid earth simulator using the Earth Simulator (ES) (35.61 Tflops/peak according to the Linpack benchmark test). It is composed of a platform and some pluggable 'analysis modules' for structural, electromagnetic thermal fluid, and wave propagation simulations. The platform includes three parts: parallel I/O interface, iterative equation solvers and visualizers. Parallel solvers have got very high performance on the ES. When using up to 176 nodes of the ES, the computational speed of the static linear analysis by the optimized ICCG (Conjugate Gradient method with Incomplete Cholesky Preconditioning) solver, has reached 3.8 TFLOPS (33.7% of peak performance of 176 nodes). Parallel visualizer can provide many visualization methods for analysis modules covering scalar, vector and tensor datasets, and have been optimized in parallel performance. The analysis modules have also been vectorized and parallelized suitably for the ES and coupled on memory with the parallel visualizer.

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SUMMARYSolid earth simulations have recently been developed to address issues such as natural disasters, global environmental destruction and the conservation of natural resources. The simulation of solid earth phenomena involves the analysis of complex structures including strata, faults, and heterogeneous material properties. Simulation of the generation and cycle of earthquakes is particularly important, but such simulations require the analysis of complex fault dynamics. GeoFEM is a parallel finite-element analysis system intended for solid earth field phenomena problems. This paper describes recent development in the GeoFEM project for the simulation of earthquake generation and cycles.