H.B. Lee

Annealing and neutron-irradiation effects on the permeability of Fe86Zr7B6Cu1

Abstract The effects of annealing and neutron irradiation on the magnetic properties of amorphous Fe 86 Zr 7 B 6 Cu 1 alloys have been investigated by means of the changes of the longitudinal permeability ratio (LPR). In general, there are no differences in magnitude and shape of the LPR curves between as-quenched amorphous and neutron-irradiated samples. This indicates that the effects of neutron irradiation on the magnetic properties of the as-quenched sample are negligible. But a drastic decrease, caused by neutron irradiation, is observed in the magnitude of the LPR and the broadening of the LPR curves of the sample annealed at 650°C, which has a maximum value of the LPR due to the presence of ultra-soft magnetic materials. This can be attributed to a decrease in domain wall displacement and to a magnetization rotation due to the neutron irradiation effect. The local anisotropy plays a significant role in the case of this sample.

Magnetization behavior and magnetoimpedance effect in melt-spun Fe75−xCoxZr8Nb2B15 (x=5, 10, 15) alloys

Abstract Soft magnetic properties of melt-spuned (Fe–Co)–Zr alloy system can be achieved upon suitable partial nanocrystallization by proper thermal treatment. In this study, we have measured the spin-wave stiffness constant, magnetoimpedance and incremental permeability ratio (PR) of Fe 75− x Co x Zr 8 Nb 2 B 15 ( x =5, 10, 15) alloys to investigate the influence of the structural changes in the nanocrystallization process as well as the changes of the magnetic properties as a function of annealing temperatures. With increasing Co content, the spin wave stiffness constant and Curie temperature increase. The full-width at half-maximum in the longitudinal PR curves do not change very much for the samples annealed at various temperatures regardless of the presence of magnetic field during the heat treatment. The broadening MI ratio curves along with increment of frequency may arise from the circumferential permeability, which is somewhat different from the longitudinal permeability.

Impacts of Seasonal Pumping on Stream-Aquifer Interactions in Miryang, Korea

Large agricultural fields in South Korea are located mostly on alluvial plains, where a significant amount of groundwater is used for heating of water-curtain insulated greenhouses. Such greenhouses are commonly used for crop cultivation during the winter dry season from November to March. After use the groundwater is discharged directly into streams, causing groundwater depletion. A hydrogeological study was carried out in a typical agricultural area of this type, located on an alluvial aquifer near the Nakdong River. Groundwater levels, chemical characteristics, and temperatures from 68 observation wells were analyzed to determine the impacts of seasonal groundwater pumping on the groundwater system and stream-aquifer interactions. Our results show that the groundwater system has not yet reached a state of dynamic equilibrium. Decades of excessive seasonal pumping have caused a gradual decline of groundwater levels, leading to groundwater depletion, especially in areas further from the river. Seasonal pumping has also significantly affected groundwater quality in the aquifer near the river. Groundwater temperature is decreasing (in this case a disadvantage), and saline groundwater is being diluted by induced recharge. The results of this study provide a basic outline for effective integrated water management that is widely applicable in South Korea.

Soft magnetic properties in Fe-based nanocrystalline alloy

Amorphous Fe 84 Zr 7 B 6 Cu 1 Al 2 and Fe 81 B 11 Nb 7 Cu 1 alloys were annealed at 723 K and 823 K for one hour to achieve good soft magnetic properties such as large magnetoimpedance ratio (MIR) and incremental permeability ratio (PR), etc. The MIR and PR of the samples were measured from 100 kHz to 10 MHz in a cryogenic chamber with temperatures from 10 K up to 300 K. The values of coercive force reveal that the optimum temperature for better soft magnetic properties is 723 K in both samples. The maximum value of MI ratio increases drastically in the Fe 81 B 11 Nb 7 Cu 1 alloy annealed at 723 K and 823 K indicating that the sample is softened by nanocrystallization. The maximum PR values of Fe 84 Zr 7 B 6 Cu 1 Al 2 alloy measured below 1 MHz show drastic increment at above 150 K due to thermal activation of magnetic domains.

Modeling Stream-Aquifer Interactions Under Seasonal Groundwater Pumping and Managed Aquifer Recharge: H. Lee et al. Groundwater xx, no. xx: xxx-xxx

In South Korea, a significant amount of groundwater is used for the heating of water-curtain insulated greenhouses during the winter dry season, which had led to problems of groundwater depletion. A managed aquifer recharge (MAR) project is currently underway with the goal of preventing such groundwater depletion in a typical cultivation area, located on an alluvial aquifer near the Nam River. In the present study, FEFLOW, a three-dimensional finite element model, was used to evaluate different strategies for MAR of the cultivation areas. A conceptual model was developed to simulate the stream-aquifer dynamics under the influence of seasonal groundwater pumping and MAR. The optimal rates and duration of MAR were assessed by analyzing the recovery of the groundwater levels and the change in the groundwater temperature. The simulation results indicate that a MAR rate of 8000 m3 /d effectively restores the groundwater level when the injection wells are located inside the groundwater depletion area. It is also demonstrated that starting the MAR before the beginning of the seasonal pumping is more effective. Riverbank filtration is preferable for securing the injection water owing to plentiful source of induced recharge from the river. Locating the pumping wells adjacent to the river where there are thick permeable layers could be a good strategy for minimizing decreases in the groundwater level and temperature.