Numerical experiments of adjusted BSSN systems for controlling constraint violations

We present our numerical comparisons between the BSSN formulation widely used in numerical relativity today and its adjusted versions using constraints. We performed three testbeds: gauge-wave, linear wave, and Gowdy-wave tests, proposed by the Mexico workshop on the formulation problem of the Einstein equations. We tried three kinds of adjustments, which were previously proposed from the analysis of the constraint propagation equations, and investigated how they improve the accuracy and stability of evolutions. We observed that the signature of the proposed Lagrange multipliers are always right and the adjustments improve the convergence and stability of the simulations. When the original BSSN system already shows satisfactory good evolutions (e.g., linear wave test), the adjusted versions also coincide with those evolutions; while in some cases (e.g., gauge-wave or Gowdy-wave tests) the simulations using the adjusted systems last 10 times as long as those using the original BSSN equations. Our demonstrations imply a potential to construct a robust evolution system against constraint violations even in highly dynamical situations.Comment: to be published in PR

Flux pinning characteristics and irreversibility line in high temperature superconductors

The flux pinning properties in high temperature superconductors are strongly influenced by thermally activated flux motion. The scaling relation of the pinning force density and the irreversibility line in various high temperature superconductors are numerically analyzed in terms of the flux creep model. The effect of two factors, i.e., the flux pinning strength and the dimensionality of the material, on these properties are investigated. It is speculated that the irreversibility line in Bi-2212 superconductors is one order of magnitude smaller than that in Y-123, even if the flux pinning strength in Bi-2212 is improved up to the level of Y-123. It is concluded that these two factors are equally important in determination of the flux pinning characteristics at high temperatures

Development of hydrogen masers for K-3 VLBI system

Two field operable hydrogen masers were developed for the VLBI joint experiment conducted by the cooperation between RRL and NASA. They are now playing an important role as the time and frequency standard of the K-3 VLBI system, which has also been developed by RRL

Parametric analysis of flux creep-flow model by using genetic algorithm

The pinning parameters for numerical calculation based on the flux creep-flow model are determined by using genetic algorithm (GA), which has been applied to many practical determination for parameters. Several estimation functions which describe the distance between the experimental and calculated results by GA were proposed, and the difference between the results were calculated. It is found that the pinning parameters of the flux creep-flow model are successfully deduced by GA. The difference between the calculated and experimental results and the calculation time are found to be largely depended on the estimation functions.Proceedings of the 24th International Symposium on Superconductivity (ISS 2011), October 24-26, 2011, Tokyo, Japa

Estimation of AC loss in cylindrical superconductor with ripple current

The loss energy density (AC loss) in cylindrical superconductor with ripple current based on Irie-Yamafuji model in which the magnetic fiel dependence of critical current density is taken into account is theoretically calculated for design of DC transmission cable system. It is confirme that the AC loss does not changed for the cases with and without DC current when the critical current does not depend on magnetic fiel which is corresponding to Bean-London model. On the contrary, it is found that there is current region where the AC loss becomes smaller than that for the case without DC current. The AC loss of ripple current is seems to be enough small in layered structure of DC transmission cable made by thin tape superconductor.Proceedings of the 24th International Symposium on Superconductivity (ISS 2011), October 24-26, 2011, Tokyo, Japa

Subsurface Flow Barriers to Reduce Nitrate Leaching

Groundwater is a very important natural resource which directly affects many human lives. In the United States, groundwater is the source of about 22 percent of the freshwater used. About 53 percent of the total population and 97 percent of the rural population use groundwater supplies for their drinking water (Moody, 1990). Although contamination of groundwater can occur naturally, agriculture is considered to be one of the most widespread nonprofit sources of groundwater contamination. Among agricultural chemicals, nitrogen-fertilizer has been used most extensively, especially by com producers. About one million tons of nitrogen-fertilizer are used annually in Iowa. In some studies, more than 50 percent of the applied fertilizer nitrogen is not removed by the crop or stored in the soil, and leaching as a form of nitrate is thought to be a major reason for the losses (Blackmer, 1987). Leached nitrate may enter groundwater supplies. Nitrate-nitrogen concentrations found in unsaturated soil below the rootzone of agricultural fields are in the range of 5 to 100 mg!L (Bouwer, 1990). Nitrate-nitrogen concentrations in tile drainage below row crops often exceed 10 mg/L, the U.S.A. drinking water standard (Gast et al., 1978; Baker and Johnson, 1981; Timmons and Dylla, 1981; Baker et al., 1985)

Countermeasures against flood damage of buildings and their applicability

In Japan, devising ways to live in areas with a possibility of flooding, to regulate and guide buildings and land use should be considered to respond to future climate change. This article investigates the cost-effectiveness of flood damage countermeasures at the building and site level based on the flood risk of the location. In the research, 3 cases were assumed; (1) when constructing a new wooden detached house, (2) when renovating an existing condominium, and (3) when a business office moves into the first floor of a RC building and a model examination of flood countermeasures was carried out and demonstrated. By calculation and comparison of “average expected payback period”, it was found reasonable to first prepare for flooding at a minimum of 30 to 50 cm above ground level, and then to consider countermeasures in stages for greater flooding depths.</p