• Journal of KIISE
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• v.44 no.8
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• pp.767-773
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• 2017

In a distributed system environment, such as a cloud database, the tail latency needs to be kept short to ensure uniform quality of service. In this paper, through experiments on a Cassandra database, we show that long tail latency is caused by a lack of memory space because the database cannot receive any request until free space is reclaimed by writing the buffered data to the storage device. We observed that, since the performance of the storage device determines the amount of time required for writing the buffered data, the performance degradation of Solid State Drive (SSD) due to garbage collection results in a longer tail latency. We propose a garbage collection synchronization technique, called SyncGC, that simultaneously performs garbage collection in the java virtual machine and in the garbage collection in SSD concurrently, thus hiding garbage collection overheads in the SSD. Our evaluations on real SSDs show that SyncGC reduces the tail latency of $99.9^{th}$ and, $99.9^{th}-percentile$ by 31% and 36%, respectively.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.5
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• pp.422-428
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• 2009

NAND flash memory is widely used in embedded systems because of many attractive features, such as small size, light weight, low power consumption and fast access speed. However, it requires garbage collection, which includes erase operations. Erase operation is slower than other operations. Further, a block has a limited erase lifetime (typically 100,000) after which a block becomes unusable. The proposed garbage collection policy focuses on minimizing the total number of erase operations, the deviation value of each block and the garbage collection time. NAND flash memory consists of pages of three types, such as valid pages, invalid pages and free pages. In order to achieve above goals, we use a page ratio to decide when to do garbage collection and to select the target victimblock. Additionally, we implement allocating method and group management method. Simulation results show that the proposed policy performs better than Greedy or CAT with the maximum rate 85% of reduction in the deviation value of the erase operations and 6% reduction in garbage collection time.

• Journal of Environmental Policy
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• v.8 no.4
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• pp.51-73
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• 2009

Although environmental education has increased in importance, few studies have been performed on the quantitative effect of environmental education on energy-saving and garbage-reducing behavior. Accordingly, this study quantitatively analyses the effect of environmental education on energy-saving and garbage-reduction. In this study, we compared reduction in energy use and garbage production between two groups, one receiving specialized and focused environmental education, and one receiving only general environmental education. We found that focused environmental education resulted in some quantifiably positive effects in encouraging energy-saving and garbage-reducing behavior. Specifically, household energy costs and amounts of school food waste for children receiving specialized environmental training were noticeably lower than those for children receiving only general environmental education. These results suggest that enhanced environmental education policy, including the launching of an environmental model school, is needed both to reduce energy use and garbage production.

• The KIPS Transactions:PartA
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• v.13A no.4 s.101
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• pp.295-304
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• 2006

Java has been established as one of the most widely-used languages owing to its support of object-oriented concepts, safety, and flexibility. Garbage collection in the Java virtual machine is a core component that relieves application programmers of difficulties related to memory management. In this paper, we propose a memory manager and a garbage collector that is implemented on a embedded java virtual machine. The memory manager divide a heap into various-sized cells and manages it as blocks of same-sized cells. So it is possible to allocate and free memory fast. We adopted the 3-color based Mark & Sweep garbage collector as our base algorithm and we propose 4-color based Mark & Sweep garbage collector for supporting multi-threaded program. The proposed garbage collector occurs memory fragmentation but we show through a experiment that the fragmentation ratio is almost fixed according as we create objects continuously.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.1191-1193
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• 2003

Water quantity and quality monitoring at Taipei Watershed Management Bureau (WRATB) is not only a daily business but also a long term job. WRATB is responsible for providing high quality drinking water to about four millions population in Taipei. The quality of drinking water provided by WRATB is among one of the best in Taiwan. The total area is 717 square kilometers. The water resource pollution is usually divided into two categories, point source pollution and nonpoint source pollution. Garbage disposal is the most important component of the point source pollution, especially those by tourist during holidays and weekends. Pesticide pollution, fertilizer pollution, and natural pollution are the major contributions for nonpoint source pollution. The objective of this paper is to implement remote sensing, geographic information systems, and global positioning systems to monitor water quantity and water quality at WRATB. There are 12 water quality monitoring stations and four water gauge stations at WRATB. The coordinates of the 16 stations were determined by GPS devices and created into the base maps. MapObjects and visual BASIC were implemented to create application modules for water quality and quantity monitoring. Water quality of the two major watersheds at WRATB was put on Internet for public review monthly. The GIS software, ArcIMS, can put location maps and attributes of all 16 stations on Internet for general public review and technical implementations at WRATB. Inquiry and statistic charts automatic manipulations for the past 18 years are also available. Garbage disposal by community and tourist were also managed by GIS and GPS. The storage, collection, and transportation of garbage were reviewed by ArcMap file format. All garbage cart and garbage can at WRATB can be displayed on the base maps. Garbage disposal by tourist during holidays and weekends can be managed by a PDA with a GPS device and a digital camera. Man power allocation for tourist garbage disposal management can be done in an integration of GIS and GPS. Monitoring of water quality and quantity at WRATB can be done on Internet and by a PDA.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.9
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• pp.617-625
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• 2009

NAND flash memory is widely used in embedded systems because of many attractive features, such as small size, light weight, low power consumption and fast access speed. However, it requires garbage collection, which includes erase operations. Erase operation is very slow. Besides, the number of the erase operations allowed to be carried out for each block is limited. The proposed garbage collection method focuses on minimizing the total number of erase operations, the deviation value of each block and the garbage collection time. NAND flash memory consists of pages of three types, such as valid pages, invalid pages and free pages. In order to achieve above goals, we use a page rate to decide when to do garbage collection and to select the target victim block. Additionally, We implement allocating method and group management method. Simulation results show that the proposed policy performs better than Greedy or CAT with the maximum rate at 82% of reduction in the deviation value of erase operation and 75% reduction in garbage collection time.

• Design Convergence Study
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• v.14 no.4
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• pp.53-64
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• 2015

The purpose of this research is to examine and find solutions with garbage problems in movie theaters for the betterment of pleasant environment to customers. The object of investigation includes three most popular movie theaters in Seoul. Analyzing current status of separating garbage and guidance notice was carried out. Also investigation of awareness on separating garbage and guidance notice has been done. The findings on inquiry are as follows. Customers tend not to separate garbage and guidance notice was not as effective. Also, separate garbage collection was very ineffective especially the food garbage. We carried out investigation on placement of guidance notice regarding recycling bin. We tried to find solutions for this problem and proposed better design. This design is emphasized on the use of particular space only. In addition, this design is focused mainly on one the three movie theaters for integration of identity. Through this design, it ought to provide clean environment and reduces inefficiencies regarding financial and time.

• Journal of the Korea Organic Resources Recycling Association
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• v.8 no.3
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• pp.73-80
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• 2000

The objective of study was to evaluate the apropriate maturity indices for garbage composting using sawdust as bulking agent. Materials used in this study were the average composition garbage(G20) and garbage conditioned by sawdust(GS30, GS50) and cereals(GSC30). Indices for evaluating maturity were VS, water soluble TOC, polysaccharide, Humification Index(HI), and E4/E6. Experiment results showed that VS reduction was the most desirable index for evaluating compost maturity except for the GS50 which were conditioned with high sawdust Water soluble TOC decreased rapidly during the composting of first one month and then little changed. Therefore, water soluble TOC was recommended as maturity index. Polysaccharide was considered as a maturity index in case of garbage conditioned with sawdust and high cereals. Humification Index(HI) and E4/E6 were available as maturity indices in case of only some garbage composting so additional study was needed to confirm them as maturity indices for all garbage composting. Correlation analysis indicated that indices for evaluating maturity of garbage(about 30 C/N ratio) adding sawdust as bulking agent and high cereals, were VS reduction, water soluble TOC, polysaccharide, and E4/E6.

• Food Science and Preservation
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• v.12 no.3
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• pp.199-203
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• 2005

Reducing sugar content of persimmon fruits was increased by applying food-garbage compost Dungsi was brighter with yellow color than that of control. The Gabjubaekmok was darker than that of control with red color. It was suggested that taste of astringent was reduced because total phenol and soluble tannin contents were reduced by applying food-garbage compost. The vitamin C content of persimmon fruits during storage was higher than that of control. Stability of persimmon fruits by applying food-garbage compost and non-food garbage compost was about the same at room temperature. At low temperature, hardness of persimmon fruits was maintained for 20 days. Hardness and reducing sugar contents of persimmon fruits were increased by applying food-garbage compost. The result was shown that there was no effect on composition of persimmon fruits by applying food-garbage compost and maintaining hardness at room temperature, but at low temperature, the composition of persimmon fruits was changed.

• The KIPS Transactions:PartA
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• v.14A no.3 s.107
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• pp.173-184
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• 2007

Garbage collection in the Java virtual machine is a core function that relieves application programmers of difficulties related to memory management. In this paper, we evaluate and analyze the performance of GenGC and GenRGC, garbage collectors for embedded Java virtual machines. For performance evaluation, we employ CVM, a real embedded Java virtual machine developed by Sun Microsystems, Inc., as a platform and also use a widely-used SpecJVM98 as a set of benchmark programs. To compare the performance of GenGC and GenRGC, we first evaluate the time of garbage collection and the delay time caused by garbage collection. Second, for more detailed performance analysis of GenRGC, we evaluate the time of garbage collection and the delay time caused by garbage collection while changing the sizes of a block and a frame. Third, we analyze the size of storage space required for performing GenRGC, and show GenRGC to be suitable for embedded environment with a limited mont of memory. Since CVM is the most representative one of embedded Java virtual machines, this performance study is quite meaningful in that we can predict the performance of garbage collectors in real application environments more accurately.