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정현환,정주노,권상주 한국정밀공학회 2015 International Journal of Precision Engineering and Vol.16 No.8
In this paper, we propose a new type of active variable stiffness actuator (VSA) by using a unique differential worm gear mechanism where a set of compressible coil springs are installed. The stiffness of the VSA is varied depending on the compressed amount of the coil springs; large compression results in an effectively stiff joint, and vice versa (compliant mode). Interestingly, an ideal rigid joint is also realizable if the springs’ reactive force is made larger than the external load (rigid mode). The VSA is characterized to become compliant rapidly if the external load exceeds the springs’ reactive force, so such a VSA can protect itself in an unexpected overloading condition. Conducted experiments confirm the effectiveness of the proposed VSA.
정현환,손경아 한국유전체학회 2014 Genomics & informatics Vol.12 No.4
Gastritis is a common but a serious disease with a potential risk of developing carcinoma. Helicobacter pylori infection isreported as the most common cause of gastritis, but other genetic and genomic factors exist, especially single-nucleotidepolymorphisms (SNPs). Association studies between SNPs and gastritis disease are important, but results on epistaticinteractions from multiple SNPs are rarely found in previous genome-wide association (GWA) studies. In this study, weperformed computational GWA case-control studies for gastritis in Korea Associated Resource (KARE) data. By transformingthe resulting SNP epistasis network into a gene-gene epistasis network, we also identified potential gene-gene interactionfactors that affect the susceptibility to gastritis.
Flowering of Adonis amurensis by Breaking Dormancy Using Gibberellins and Cytokinins
정현환,김기선 한국원예학회 2011 Horticulture, Environment, and Biotechnology Vol.52 No.3
Amur adonis (Adonis amurensis) was used for the study of PGRs responses on the dormancy breaking and flowering. All plant treated with GA_3 or GA_(4+7) showed earlier sprouting by breaking the dormancy and resulted to fast flowering, irrespective of concentration. Plant height and the number of nodes tent to be increased by GAs application on dormant plant. Among the different kinds of GA treatments, GA_(4+7) was most effective in dormancy breaking and flower emergence with the effect of higher plant height and increased node number rather than GA_3. However, GA_(4+7) showed several disadvantages such as reducing the flowering rate and induced the overgrowth that resulting in stretched weak plants. Beside GA, cytokinins such as TDZ showed clear effect of dormancy breaking but, other cytokinins such as BAP and Kinetin showed no clear positive effects in breaking the dormancy. Dormant amur adonis treated with BAP and Kinetin flowered without leaf emergency and subsequent shoot growth resulted in showing abnormal flowering and growth, but it treated with TDZ showed the normal flowering with shoot growth, but flowering percentage was very low. In conclusion, we could recommend that 100-500 mg・L^(-1) GA_3 application as an alternative method to chilling treatment for breaking dormancy and normal flowering of A. amurensis. And we could also recommend 20 or 50 mg・L^(-1) TDZ for the dormancy break and subsequent shoot growth, but not for flowering.
Chilling Requirements for Dormancy Breaking and Flowering of Adonis amurensis Regel et Radde
정현환,김기선 한국원예학회 2009 Horticulture, Environment, and Biotechnology Vol.50 No.6
Dormancy breaking and flowering of Adonis amurensis were controlled by the forcing date and cold storage in the central region of Korea, Suwon. Bud break and flowering did not occur throughout the experiment when dormant rootstocks were transferred to a greenhouse on October 22, 2002, in which natural accumulative chilling (NAC) was 0 h. Days to bud break and flowering from transferring date were shortened as transferring date was delayed. Bud break and flowering percentage, plant height, and number of leaves per plant at flowering were increased with delayed transferring date. Approximately ≥ 92% of plants flowered normally with shoot growth when transferred after December 20 (= 1,200 h NAC). Prolonged cold storage also promoted bud break and flowering of dormant A. amurensis. Approximately 90% of rootstocks began to sprout within 10 days with normal flowering and subsequent growth after flowering when stored for at least 6 weeks (= 1,008 h AC) irrespective of temperature. This result was comparable with those transferred from an open field to greenhouse on December 20 (= 1,200 h NAC). Twelve weeks of cold storage, except 0℃, induced the bud elongation and sprouting during cold storage, resulting in overgrowth and weak plants. As a result, at least 1,200 h NAC or 6 weeks of cold storage (= 1,008 h AC) below 10℃ could be recommended as forcing methods for dormancy breaking, normal flowering, and subsequent growth of dormant A. amurensis in the central region of Korea. However, since constant cold storage was more effective than fluctuating chilling temperature in the natural environment, 6 weeks of cold storage is recommended for forcing method of A. amurensis and 0℃ as the storage temperature for longer duration than 12 weeks in order to prevent shoot growth during cold storage.
Virtual Joint Method for Kinematic Modeling of Wheeled Mobile Manipulators
정현환,김형식,김희국,정주노 제어·로봇·시스템학회 2014 International Journal of Control, Automation, and Vol.12 No.5
In this paper, we propose a virtual joint method that better utilizes quasi-velocities for the kinematic modeling of wheeled mobile manipulators. By identifying quasi-velocities as motions of imaginary revolute and prismatic kinematic pairs, our method enables one to regard a mobile manipulator as an ordinary articulated manipulator for the purposes of velocity analysis. We also propose an inverse kinematic scheme for the mobile manipulators along the line with the virtual joint based kinematic framework. Details are worked out for mobile manipulators with representative differential-drive and car-like mobile platforms.
Effect of Rooting Promoters on the Rooting and Growth of Cuttings in Several Flowering Shrubs
정현환,박기영,권오현,유봉식 인간식물환경학회 2017 인간식물환경학회지 Vol.20 No.5
This study was conducted to investigate the effects of rooting promoters on rooting and seedling quality in Buddleja davidii ‘Empire Blue’, Hydrangea paniculata ‘Magical Candle’, Hydrangea arborescence ‘Annabelle’, Stephanandra incisa semi-hardwood cuttings. IAA and IBA (500, 1000, or 1500 mg・L-1 soaking for 30 minutes and 3,000 mg・L-1 dipping for 10 seconds) or RootoneTM were used as rooting promoter. In B. davidii ‘Empire Blue’, IBA 1,500 mg・L-1 soaking reduced rooting percentage than control, but the effect of rooting promoters was generally insignificant. Number of leaves and shoot length were reduced in RootoneTM and IBA 1,500, 3,000 mg・L-1 treatments. IAA 1,000~3,000 mg・L-1 and IBA 500 mg・L-1 treatments showed better mat formation than control. The rooting ratio of H. paniculata ‘Magical Candle’ increased to 66.7% in IBA 1,500 mg・L-1 soaking treatment compared with 26.4% in the control. The mat formation was higher in RootoneTM, IAA and IBA treatments compared to control, and root length showed longer tendency in IAA and IBA except RootoneTM. The rooting ratio of H. arborescence ‘Annabelle’ was highest at 70.8% in the control and auxin treatments showed negative effect on the rooting percentage except IAA 1,000 mg・L-1 soaking treatment. The mat formation was very poor in IBA 1,000 and 1,500 mg・L-1 soaking at 1.1 and 1.3, respectively. S. incisa showed high rooting percentage at RootoneTM (80%) and IAA 1,500 mg・L-1 (80%) treatments compared to control (51.7%). Root length and dry weight were high in IAA 1,500 mg・L-1 soaking treatment. As a result, B. davidii ‘Empire Blue’ and H. arborescence ‘Annabelle’ did not need rooting promoter for stem cuttings, and IBA 1,500 mg・L-1, IAA 1,500 mg・L-1 soaking treaments could be used to improve rooting and seedling quality of H. paniculata ‘Magical Candle’ and S. incisa semi-hardwood cuttings, respectively.