Search

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, atmospheric simulation models have improved our understanding of the atmospheric behavior of radionuclides. Model intercomparisons provide valuable and useful information for evaluating the validity and variability of individual model results. In this study, we compared results of seven atmospheric transport models used to simulate 137Cs released from the FDNPP to the atmosphere. All model results used in this analysis had been submitted for a model intercomparison project of the Science Council of Japan (2014, http://www.scj.go.jp/en/report/index.html). Here we assessed model performance by comparing model results with observed hourly atmospheric concentrations of 137Cs, with a particular focus on nine plumes over the Tohoku and Kanto regions. The intercomparison results showed that model performance in reproducing 137Cs concentrations was highly variable among different models and plumes. In general, models better reproduced plumes that passed over many observation stations. The performance among the models was consistent with the simulated wind fields and the source terms used. We also assessed model performance in relation to accumulated 137Cs deposition. Simulated areas of high 137Cs deposition were consistent with the simulated 137Cs plume pathways, though the models that best simulated atmospheric 137Cs concentrations were different from those that best simulated deposition. The ensemble mean of all models consistently reproduced atmospheric 137Cs concentrations and deposition well, suggesting that use of a multimodel ensemble results in more effective and consistent model performance. An intercomparison of seven simulation models for atmospheric 137Cs concentration and deposition was performedModel performance in reproducing observed 137Cs concentrations in air was highly variable among different models and plumesThe multimodel ensemble showed the best model performance and consistency in reproducing 137Cs concentrations and deposition

Abstract: Using the checkerboard titration method as well as the time-kill curve technique, we investigated the activities of β-lactams, fluoroquinolones, amikacin, and fosfomycin alone and in combination against Pseudomonas aeruginosa isolated from patients with complicated urinary tract infections. In the checkerboard titration studies, none of 21 combinations demonstrated antagonism against 26 strains tested, and the mean fractional inhibitory concentration (FIC) indices for these combinations ranged between 0.4694 and 0.9828. Corresponding to the respective FIC indices, the bactericidal activity determined in combinations of meropenem with ciprofloxacin or amikacin and ceftazidime with ciprofloxacin at sub-minimum inhibitory concentrations (MICs) produced a great reduction in bacterial counts (≥2 log10 CFU/ml) within 6 h of administration against most of the strains, including strains resistant to one or both drugs, and these synergistic effects were confirmed morphologically by scanning electron microscopy. In time-lag combinations, the first administration of ciprofloxacin or amikacin supplemented by meropenem with 1-h lag diminished bactericidal activity, in comparison with the simultaneous administration of the drugs. These results suggest that simultaneous combinations of β-lactams with fluoroquinolones or amikacin may be useful alternatives for the treatment of serious infections due to P. aeruginosa.

A low-solidity circular cascade, conformally transformed from a high-stagger linear cascade of double-circular-arc vanes with solidity 0.69, was tested as a part of diffuser systems of a transonic centrifugal compressor and the static pressures were measured around a vane of the cascade and on the side wall between cascade vanes in detail. The blade loading of cascade vane was discussed by integrating the pressure distribution around the vane. The experimental data for lift-coefficient of vane were almost on a single straight line with positive gradient against angle-of-attack over a wide range of inflow Mach number and inflow angle. The maximum lift coefficient reached about 1.5 and the vane worked well to the surge condition of the compressor. The structure of shock wave was also discussed by drawing a contour map of the flow Mach number between cascade vanes. The normal shock wave was observed on the suction surface of vane and it moved upstream along the suction surface with the decrease in inflow angle. The vane did not fall in stall even though the Mach number upstream of the shock wave was over 1.4.

An impeller of a supersonic centrifugal compressor was tested in a casing without a diffuser so that the flow range was not limited by the diffuser. Regarding the impeller, emphasis was placed on critical conditions such as inducer stall and surge. Experimental data were examined based on a one-dimensional analysis and a quasi-three-dimensional analysis. Furthermore, the variation of shroud pressure with respect to time at many locations was utilized to guess the details of flow behavior between impeller blades near the shroud, and the contour of isobars was compared with that predicted by a quasi-three-dimensional analysis. When the inlet relative velocity was supersonic, a detached shock wave and a shock wave in a blade channel were recognized, but the compressor operated efficiently, although such condition existed only in a narrow flow range limited by surge and choke.

An analytical study has been made to clarify the details of the flow between a rotating disk and a stationary casing side-wall with and without an axisymmetric inward through-flow. The flow field between the casing side-wall and the surface of the rotating disk is divided into four layers instead of three in earlier analyses. Proceeding from the casing side-wall to the disk, they are a wall boundary layer, an outward-flow layer, a core and a disk boundary layer. The flow field is determined so that the integrated equations of motion as well as the continuity equation are satisfied for each of the four layers. In the present analysis, least empirical informations relative to a rotating disk are used compared with the theories in the literature. The mechanics of the flow field is explained by the flow model without contradiction, and the predicted radial and axial distributions of velocity and the pressure distribution in the casing agree well with experimental results.

A low-solidity circular cascade, conformally transformed from a high-stagger linear cascade of double-circular-arc vanes with solidity 0.69, was tested as a part of diffuser systems of a transonic centrifugal compressor and the static pressures were measured around a vane of the cascade and on the side wall between cascade vanes in detail. The blade loading of cascade vane was discussed by integrating the pressure distribution around the vane. The experimental data for lift-coefficient of vane were almost on a single straight line with positive gradient against angle-of-attack over a wide range of inflow Mach number and inflow angle. The maximum lift coefficient reached about 1.5 and the vane worked well to the surge condition of the compressor. The structure of shock wave was also discussed by drawing a contour map of the flow Mach number between cascade vanes. The normal shock wave was observed on the suction surface of vane and it moved upstream along the suction surface with the decrease in inflow angle. The vane did not fall in stall even though the Mach number upstream of the shock wave was over 1.4.

The flow field in the inducer of a high-pressure-ratio centrifugal compressor has been measured with a laser-2-focus velocimeter (L2FV) at two flow rates that were on each side of the apparent inducer-stall limit at 70 percent speed. The limit was determined based on the pressure pattern between inducer blades along the shroud. The measured time-mean velocity distribution is compared with the prediction based on an inviscid quasi-three-dimensional flow analysis and the viscous effects are clarified. Furthermore, the nature of flow unsteadiness is discussed on the basis of the L2FV data. Using the observed data it is concluded that the inducer works well even at the apparent inducer-stall condition.

In radial turbines with variable nozzles, the flow downstream of the nozzles could be distorted by the leakage flow through the tip clearance of the upstream nozzle vanes. To investigate the effects of flow distortion on the performance of turbine rotors, two rotors with different numbers of blades were tested for three types of distorted velocity distribution at the rotor inlet. In the case of the 20-blade rotor with moderate blade loading, the flow distortion at the rotor inlet had a negligible effect on the rotor characteristics, and the measured data on the turbine performances agreed well with prediction. Predictions were made with a conventional one-dimensional flow model applied to the rotor flow, while a two-layer flow model was applied to the flow in the nozzle with clearance. In the case of the 10-blade rotor with heavy blade loading, however, the rotor performance was found to be sensitive to the inlet flow distortion and was considerably lower than the prediction.

Low-solidity circular cascades, conformally transformed from high-stagger linear cascades of double-circular-arc vanes with solidity 0.69, were used as a part of the diffuser system of a transonic centrifugal compressor. Performance test results were compared with data of the same compressor with a vaneless diffuser. Good compressor performance and a wider flow range as well as a higher pressure ratio and a higher efficiency, superior to those with a vaneless diffuser, where the flow range was limited by choke of the impeller, were demonstrated. The test circular cascade diffusers demonstrated a good pressure recovery over a wide range of flow angles, even when the inflow Mach number to the cascade was over unity.

In radial turbines with variable nozzles, the flow downstream of the nozzles could be distorted by the leakage flow through the tip clearance of the upstream nozzle vanes. To investigate the effects of flow distortion on the performance of turbine rotors, two rotors with different numbers of blades were tested for three types of distorted velocity distribution at the rotor inlet. In the case of the 20-blade rotor with moderate blade loading, the flow distortion at the rotor inlet had a negligible effect on the rotor characteristics, and the measured data on the turbine performances agreed well with prediction. Predictions were made with a conventional one-dimensional flow model applied to the rotor flow, while a two-layer flow model was applied to the flow in the nozzle with clearance. In the case of the 10-blade rotor with heavy blade loading, however, the rotor performance was found to be sensitive to the inlet flow distortion and was considerably lower than the prediction.

Low-solidity circular cascades, conformally transformed from high-stagger linear cascades of double-circular-arc vanes with solidity 0.69, were used as a part of the diffuser system of a transonic centrifugal compressor. Performance test results were compared with data of the same compressor with a vaneless diffuser. Good compressor performance and a wider flow range as well as a higher pressure ratio and a higher efficiency, superior to those with a vaneless diffuser, where the flow range was limited by choke of the impeller, were demonstrated. The test circular cascade diffusers demonstrated a good pressure recovery over a wide range of flow angles, even when the inflow Mach number to the cascade was over unity.