Background: This study was undertaken to analyze the distribution and ecological characteristics of invasive alien plant species on Jeju Island, and to provide basic data for their management and control. Results: A field research was conducted at 436 locations on Jeju Island. The field research identified nine species of invasive alien species growing on Jeju Island. Based on the distribution pattern, Hypochaeris radicata L., Rumex acetosella, and Ambrosia artemisiifolia L. were found to be distributed horizontally throughout Jeju Island, with vertical growth in two or more vegetation zones, from warm temperate to the subalpine zone. Widely distributed species penetrate various habitats, such as grasslands, ranches, roadsides, farmlands, and empty lots, and have an immensely negative impact on the ecosystem, including declining biodiversity on Jeju Island. Paspalum distichum var. indutum Shinners, Paspalum distichum L., Solanum carolinense L., and Aster pilosus Willd. were distributed in some areas as a biased distribution species, whereas Lactuca scariola L. and Solidago altissima L. were found only in certain areas as centralized distribution species. Conclusions: The centralized distribution species and biased distribution species of the invasive plants in the ecosystem of Jeju Island should be physically eliminated, keeping in mind the short-and mid-term perspectives and monitoring, and by considering expansion of additional distribution areas. Due to limitations of physical/ chemical elimination, time, and cost, widely distributed species require to be eliminated and managed, mainly to restore the integrity of the ecosystem, by planting native species to reestablish the habitat.
In recent years, a large portion of smartphone applications (Apps) has targeted context-aware services. They aim to perceive users' real-time context like his/her location, actions, or even emotion, and to provide various customized services based on the inferred context. However, context-awareness in mobile environments has some challenging issues due to limitations of devices themselves. Limited power is regarded as the most critical problem in context-awareness on smartphones. Many studies have tried to develop low-power methods, but most of them have focused on the power consumption of H/W modules of smartphones such as CPU and LCD. Only a few research papers have recently started to present some S/W-based approaches to improve the power consumption. That is, previous works did not consider energy consumed by context-awareness of Apps. Therefore, in this paper, we focus on the power consumption of context-aware Apps. We analyze the characteristics of context-aware Apps in a perspective of the power consumption, and then define two main factors which significantly influence the power consumption: a sort of context that context-aware Apps require for their services and a type of ways that a user uses them. The experimental result shows the reasonability and the possibility to develop low-power methods based on our analysis. That is, our analysis presented in this paper will be a foundation for energy-efficient context-aware services in mobile environments.
Abstract：Electric propulsion motors are operated from a variable frequency drive, which supplies power to motors at a frequency appropriate to the desired speed. The objective of this study was to evaluate power converters for shipboard applications and to recommend converters that meet lower harmonic distortion levels and torque ripples. Two systems were studied in detail : Cyclo-converters and PWM-converters. Cyclo-converters are the obvious choice where size, weight and efficiency are the most critical issues. However they have a disadvantage in power factor and they produce severe torque ripples in the motor which makes them unacceptable without special systems.PWM-converters produces better motor current waveform and eliminates common mode voltage issues at the motor, but suffers a multiple stages of power conversion and the isolating transformer. Results of this case study show that PWM-converters are more advanced and efficient drives for induction motor of electric propulsion ship.
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