• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.125-135
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• 1998

This study presents a design method for three-span continuous preflex composite girder bridges (3S-PCB) which imposes prestresses in the negative moment region by lifting or lowering interior supports and the design method is automated by a computer program which incorporates optimal design procedure. The objective function for the design of 3S-PCB minimizes the cost of construction materials and the constraint functions represent the limited dimensions of the design section and the allowable stress for each structural member as given in the specifications. Optimal design procedure used in this study is a modification of existing sequential unconstrained minimization technique (SUMT), a numerical analyses procedure for two-span continuous preflex composite bridges. The optimized design sections determined for each span length are compared with those of simple preflex composite beams (SPCB) and the optimal girder depth is determined by defining the relationship between girder depth and construction material costs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1819-1826
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• 1996

This paper present the claculating method of optimum correction mass within permissible vibration linits for ratating machinery in two-plane field balancing. Basic technique of this method is based on influence coefficient method, and grphic vector composition that the resultant of two influence vectors obtained by trial mass have to be equilibrium with initial vibration vector in the each correction plane. Genetic algorithm which is a search algorithm based on the mechanism of natural selection and natural genetics is sued for vector composition, and SUMT method is used to objective function which seeks optimum correction mass for balancing a rotor.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.1
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• pp.91-95
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• 2008

Flash memory is widely used in embedded systems because of its benefits such as non-volatile, shock resistant, and low power consumption. But NAND flash memory suffers from out-place-update, limited erase cycles, and page based read/write operations. To solve these problems, log-structured filesystem was proposed such as YAFFS. However, YAFFS sequentially retrieves an array of all block information to allocate free block for a write operation. Also before the write operation, YAFPS read the array of block information to find invalid block for erase. These could reduce the performance of the filesystem. This paper suggests fast operation method for NAND flash filesystem that solves the above-mentioned problems. We implemented the proposed methods in YAFFS. And we measured the performance compared with the original technique.

• The KIPS Transactions:PartA
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• v.18A no.4
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• pp.135-142
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• 2011

This research is to design an effective buffer structure and its management for flash memory based high performance SSDs (Solid State Disks). Specifically conventional SSDs tend to show asymmetrical performance in read and /write operations, in addition to a limited number of erase operations. To minimize the number of erase operations and write latency, the degree of interleaving levels over multiple flash memory chips should be maximized. Thus, to increase the interleaving effect, an effective buffer structure is proposed for the SSD with a hybrid address mapping scheme and super-block management. The proposed buffer operation is designed to provide performance improvement and enhanced flash memory life cycle. Also its management is based on a new selection scheme to determine random and sequential accesses, depending on execution characteristics, and a method to enhance the size of sequential access unit by aggressive merging. Experiments show that a newly developed mapping table under the MBA is more efficient than the basic simple management in terms of maintenance and performance. The overall performance is increased by around 35% in comparison with the basic simple management.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.11
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• pp.599-609
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• 2007

Due to the restrictions of Flash memory such as overwrite limitation and write/erase operational unit differences, block cleaning is required in Flash memory based file systems and known as a key factor on the performance of file systems. In this paper, we identify three parameters, namely utilization, invalidity and uniformity, and analyze how the parameters affect the cost of block cleaning. The analysis show that as uniformity degrades, the cost of block cleaning increases drastically. To overcome this problem, we design a new modification-aware(MODA) page allocation scheme that strives to keep uniformity high by separating frequently-updating data from infrequently-updating data. Real implementation experiments conducted on an embedded system show that the MODA scheme can actually enhance uniformity of Flash memory, which consequently leads to reduce the cost of block cleaning with an average of 123%, compared to the traditional sequential allocation scheme that is used in YAFFS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.405-419
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• 2012

In this paper, we propose a joint base station(BS) and relay precoders design in multi-relay aided multi-user all-multiple-input multiple-output(MIMO) system. The design criterion is to minimize user sum mean square error(SMSE) with relay sum power constraint(RSPC) where only local channel state information(CSI)s are available at relays. Local CSI at a relay is defined as the CSI of the channel which the relay itself accesses, out of among all the 1st hop and the 2nd hop channel in the system. With BS precoder structure which is concatenated with block diagonalization(BD) precoder, each relay can determine its own precoder using only local CSI. Proposed scheme is based on sequential iteration of two stages; stage 1 determines BS precoder and relay precoders jointly with SMSE duality, and stage 2 determines user receivers. Proposed scheme can be demonstrated theoretically to be always converge. We verify that proposed scheme outperforms simple amplify-and-forward(SAF), MMSE relay, and proposed schemes in [1] in terms of both SMSE and sum-rate performances.