• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.1
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• pp.58-64
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• 2004

This paper proposes a novel control scheme for the harmonic reduction of DC power regenerating systems, which can regenerate the excessive DC power from DC bus line to AC supply in subway systems. In the developed regenerating systems controlled by MAC(Modified a-Conduction) method, the order of remaining harmonics are 12k$\pm$1. In SHE(Selected Harmonic Elimination) method proposed in this paper, however, the l1th and 13th harmonics are additionally eliminated. And moreover 23rd harmonics, lowest order harmonics among the remaining harmonics, is eliminated by 23rd AC filter furnished at the output terminals of regenerating systems. To verify the validity of the proposed SHE-based harmonic reduction technique, computer simulations are carried out. Simulation results show that the THDs of output voltages are lower than that of the MAC method and the THDs in the control range are in the range of 0.53-0.68 percents.

• Korean Journal of Weed Science
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• v.1 no.1
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• pp.52-56
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• 1981

A 2-year field experiment was conducted to determine the influence of early and late soybean (Clycine max Merr) seeding times on competitive relationships between soybeans and annual weeds. Soybeans were planted on May 20 and June 20. Durations of weed competition and weed control were 0, 3, 6, 9, and 12 weeks after planting sad for full growing season. Dominant weeds were Portulaca oleracia, Centipeda minima, Rorippa cantonienais, Chenopodium album, Acalypha australis, Echinochloa crusgalli, and Digitaria sanguinalis. The dry weight of weeds increased with extended competition, especially at early seeding time of soybeans. Soybean yields were decreased as duration of weed competition was extended. More severe yield reduction occurred at late-planted soybeans with early stage weed competition but at early-planted soybeans when weeds competed with soybeans for a 2 weeds and full growing season. The dry weight of weeds emerged after weeding was decreased at early and late seeding times of soybeans as duration of weed control was prolonged. Soybean yields decreased with shortening duration of weed control end this trend of yield reduction was slightly more remarkable at late-planted soybeans than at early-planted soybeans. Late-planted soybeans were required longer than 6 weeks of weed control period to achieve maximum yield as compared to early-planted soybeans.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.333-342
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• 2012

This paper presents a vowel onset point (VOP) detection method based on the human auditory system. This method maps the "perceptual" frequency scale, i.e. Mel scale onto a linear acoustic frequency, and then establishes a series of Triangular Mel-weighted Filter Bank simulate the function of band pass filtering in human ear. This nonlinear critical-band filter bank helps greatly reduce the data dimensionality, and eliminate the effect of harmonic waves to make the formants more prominent in the nonlinear spaced Mel spectrum. The sum of mel spectrum peaks energy is extracted as feature for each frame, and the instinct at which the energy amplitude starts rising sharply is detected as VOP, by convolving with Gabor window. For the single-word database which contains 12 vowels articulated with different kinds of consonants, the experimental results showed a good average detection rate of 72.73%, higher than other vowel detection methods based on short-time energy and zero-crossing rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.2
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• pp.425-431
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• 2011

The harmonic distortion level may be significant in electric propulsion systems, as the main loads usually are variable speed propulsion/thruster drives. Distortion of currents and supply voltage waveforms may lead to: Increased power dissipation(losses) in equipment connected to the network, such as generators, motors, transformers, cables, etc., from the harmonic currents, may cause overheating and deterioration of the insulation, and reduced life time of the equipment. In this paper introduced the canceling method of harmonic currents by a multipulse drive with phase shifting transformer. The simulation results indicated a good speed response to the middle speed range of electric propulsion motor. And also, THD(total harmonic distortion) and torque ripple could be reduced in comparing the 12-pulse drive with 6-pulse drive.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.25 no.1
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• pp.77-86
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• 1980

Asking to change the cropping patterns to save the labor and capitals in paddy rice cultivation, the study was intended to know the weed problems under the various possible cultural systems; namely, direct seeding (in broadcast and row), machine transplanting and hand transplanting. Under the conditions as weedy check plots, paddy yields were significantly variated among cropping systems, and the functions of panicle No. and spikelet No. to the yield were neglected, among others. However, the yield and yield components were narrowed among cropping systems, and the function of spikelets number per area was comparatively improved to the others.

• Current Research on Agriculture and Life Sciences
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• v.17
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• pp.21-29
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• 1999

This study was carried out to determine the promising method for the production of mother bulbs using garlic bulbs at the experimental field of Ange high school, Eusung in Korea from 1996 to 1998. The bulbs and bulbils were taken from a local cultivar 'Eusung' garlic. The growth of bulbil and yield potential were compared with different harvesting times and cultivation methods of bulbil. The harvesting time of bulbils which were capable of producing the mother bulbs was ranged from 15 days to 30 days after the emergence of flower stalks. The best results based on the yield and number of bulbs were obtained from the bulbils sampled at the just before garlic harvesting, 30 days after flower-stalk emergence. The mulching with transparent polyethylene(PE) film in bulbil cultivation was more effective for the plant growth and bulb formation than that with black PE film. The PE mulching from 30 days after seeding of bulbils to 30 days (late-April) before bulb harvesting was the moot effective for the increase of bulb yield. In the cultivation of garlic bulbils, application of lime (150 kg/10a) and compost (3,000 kg/10a) without any chemical fertilizers produced more bulbs in comparison with the standard level of fertilizer (N - $P_2O_5$ - $K_2O$ - compost - lime = 24.8 - 8.0 - 19.2 - 3,000 - 150 kg/10a). It was determined that the involucre seeding and assemble seeding of bulbils was effective and labour-saving methods for the production of mother bulbs from garlic bulbils. Input of labour force for the involucre seeding was decreased up to 61% as compared with the conventional drill seeding of bulbils. Mean yield from the cultivation of bulbil-derived single cloves was remarkably increased up to 95% in comparison with that of the common cloves. The larger size of single clove produced more yields, and the optimum planting density of single clove was $20{\times}10cm$. The cloves differentiated directly from bulbil showed to have higher yield potential than that from common cloves.